diff --git a/main/src/main/java/org/mobilitydata/gtfsvalidator/table/GtfsRouteNetworkSchema.java b/main/src/main/java/org/mobilitydata/gtfsvalidator/table/GtfsRouteNetworkSchema.java
new file mode 100644
index 0000000000..fb14d1257f
--- /dev/null
+++ b/main/src/main/java/org/mobilitydata/gtfsvalidator/table/GtfsRouteNetworkSchema.java
@@ -0,0 +1,17 @@
+package org.mobilitydata.gtfsvalidator.table;
+
+import org.mobilitydata.gtfsvalidator.annotation.*;
+
+@GtfsTable("route_networks.txt")
+public interface GtfsRouteNetworkSchema extends GtfsEntity {
+  @FieldType(FieldTypeEnum.ID)
+  @ForeignKey(table = "routes.txt", field = "route_id")
+  @Required
+  @PrimaryKey
+  String routeId();
+
+  @FieldType(FieldTypeEnum.ID)
+  @ForeignKey(table = "networks.txt", field = "network_id")
+  @Required
+  String networkId();
+}
diff --git a/main/src/main/java/org/mobilitydata/gtfsvalidator/validator/NetworkIdConsistencyValidator.java b/main/src/main/java/org/mobilitydata/gtfsvalidator/validator/NetworkIdConsistencyValidator.java
new file mode 100644
index 0000000000..610ce4d4fb
--- /dev/null
+++ b/main/src/main/java/org/mobilitydata/gtfsvalidator/validator/NetworkIdConsistencyValidator.java
@@ -0,0 +1,81 @@
+package org.mobilitydata.gtfsvalidator.validator;
+
+import static org.mobilitydata.gtfsvalidator.notice.SeverityLevel.ERROR;
+
+import javax.inject.Inject;
+import org.mobilitydata.gtfsvalidator.annotation.GtfsValidationNotice;
+import org.mobilitydata.gtfsvalidator.annotation.GtfsValidator;
+import org.mobilitydata.gtfsvalidator.notice.NoticeContainer;
+import org.mobilitydata.gtfsvalidator.notice.ValidationNotice;
+import org.mobilitydata.gtfsvalidator.table.*;
+
+@GtfsValidator
+public class NetworkIdConsistencyValidator extends FileValidator {
+  private final GtfsRouteTableContainer routeTableContainer;
+  private final GtfsRouteNetworkTableContainer routeNetworkTableContainer;
+
+  private final GtfsNetworkTableContainer networkTableContainer;
+
+  @Inject
+  NetworkIdConsistencyValidator(
+      GtfsRouteTableContainer routes,
+      GtfsRouteNetworkTableContainer routeNetworks,
+      GtfsNetworkTableContainer networks) {
+    this.routeTableContainer = routes;
+    this.routeNetworkTableContainer = routeNetworks;
+    this.networkTableContainer = networks;
+  }
+
+  @Override
+  public void validate(NoticeContainer noticeContainer) {
+    // Validate the presence of network_id in routes and its specification in either route_network
+    // or network files
+    boolean hasNetworkIdField = this.routeTableContainer.hasColumn(GtfsRoute.NETWORK_ID_FIELD_NAME);
+    if (hasNetworkIdField) {
+      if (!this.routeNetworkTableContainer.isMissingFile()) {
+        noticeContainer.addValidationNotice(
+            new RouteNetworksSpecifiedInMoreThanOneFileNotice(
+                GtfsRoute.FILENAME, GtfsRouteNetwork.FILENAME, GtfsRoute.NETWORK_ID_FIELD_NAME));
+      }
+      if (!this.networkTableContainer.isMissingFile()) {
+        noticeContainer.addValidationNotice(
+            new RouteNetworksSpecifiedInMoreThanOneFileNotice(
+                GtfsRoute.FILENAME, GtfsNetwork.FILENAME, GtfsRoute.NETWORK_ID_FIELD_NAME));
+      }
+    }
+  }
+
+  /**
+   * Indicates that route network identifiers are specified across multiple files.
+   *
+   * <p>This notice highlights a data integrity issue where route network specifications are
+   * redundantly defined in more than one file. According to specifications, a route network
+   * identifier should be uniquely defined in a single file. Any additional definitions of route
+   * network specifications in other files are considered conditionally forbidden.
+   */
+  @GtfsValidationNotice(
+      severity = ERROR,
+      files =
+          @GtfsValidationNotice.FileRefs({
+            GtfsRouteSchema.class,
+            GtfsRouteNetworkSchema.class,
+            GtfsNetworkSchema.class
+          }))
+  static class RouteNetworksSpecifiedInMoreThanOneFileNotice extends ValidationNotice {
+    /** Name of the field in fileNameA */
+    private final String fieldName;
+
+    /** The name of the first file. */
+    private final String fileNameA;
+
+    /** The name of the second file which presence duplicates route networks specification. */
+    private final String fileNameB;
+
+    RouteNetworksSpecifiedInMoreThanOneFileNotice(
+        String filename1, String filename2, String fieldName) {
+      this.fileNameA = filename1;
+      this.fileNameB = filename2;
+      this.fieldName = fieldName;
+    }
+  }
+}
diff --git a/main/src/test/java/org/mobilitydata/gtfsvalidator/validator/NetworkIdConsistencyValidatorTest.java b/main/src/test/java/org/mobilitydata/gtfsvalidator/validator/NetworkIdConsistencyValidatorTest.java
new file mode 100644
index 0000000000..0dfe65a6d2
--- /dev/null
+++ b/main/src/test/java/org/mobilitydata/gtfsvalidator/validator/NetworkIdConsistencyValidatorTest.java
@@ -0,0 +1,86 @@
+package org.mobilitydata.gtfsvalidator.validator;
+
+import static com.google.common.truth.Truth.assertThat;
+
+import com.google.common.collect.ImmutableList;
+import org.junit.Before;
+import org.junit.Test;
+import org.mobilitydata.gtfsvalidator.notice.NoticeContainer;
+import org.mobilitydata.gtfsvalidator.parsing.CsvHeader;
+import org.mobilitydata.gtfsvalidator.table.*;
+
+public class NetworkIdConsistencyValidatorTest {
+
+  private NoticeContainer noticeContainer;
+  private GtfsRouteTableContainer routeTableContainer;
+  private GtfsRouteNetworkTableContainer routeNetworkTableContainer;
+  private GtfsNetworkTableContainer networkTableContainer;
+
+  @Before
+  public void setup() {
+    noticeContainer = new NoticeContainer();
+    routeTableContainer =
+        GtfsRouteTableContainer.forHeaderAndEntities(
+            new GtfsRouteTableDescriptor(),
+            new CsvHeader(ImmutableList.of("route_id", "network_id").toArray(new String[0])),
+            ImmutableList.of(
+                new GtfsRoute.Builder().setRouteId("123").setNetworkId("network1").build()),
+            noticeContainer);
+    routeNetworkTableContainer =
+        new GtfsRouteNetworkTableContainer(
+            new GtfsRouteNetworkTableDescriptor(), GtfsTableContainer.TableStatus.MISSING_FILE);
+    networkTableContainer =
+        new GtfsNetworkTableContainer(
+            new GtfsNetworkTableDescriptor(), GtfsTableContainer.TableStatus.MISSING_FILE);
+  }
+
+  @Test
+  public void validatesConditionalForbiddenFilePresenceNoNotice() {
+    NetworkIdConsistencyValidator validator =
+        new NetworkIdConsistencyValidator(
+            routeTableContainer, routeNetworkTableContainer, networkTableContainer);
+    validator.validate(noticeContainer);
+    assertThat(noticeContainer.getValidationNotices().isEmpty());
+  }
+
+  @Test
+  public void validatesConditionalForbiddenFilePresence1() {
+    routeNetworkTableContainer =
+        GtfsRouteNetworkTableContainer.forEntities(
+            ImmutableList.of(
+                new GtfsRouteNetwork.Builder().setRouteId("123").setNetworkId("network1").build()),
+            noticeContainer);
+    NetworkIdConsistencyValidator validator =
+        new NetworkIdConsistencyValidator(
+            routeTableContainer, routeNetworkTableContainer, networkTableContainer);
+    validator.validate(noticeContainer);
+    assertThat(noticeContainer.getValidationNotices().size() == 1);
+    NetworkIdConsistencyValidator.RouteNetworksSpecifiedInMoreThanOneFileNotice notice =
+        (NetworkIdConsistencyValidator.RouteNetworksSpecifiedInMoreThanOneFileNotice)
+            noticeContainer.getValidationNotices().get(0);
+    NetworkIdConsistencyValidator.RouteNetworksSpecifiedInMoreThanOneFileNotice expectedNotice =
+        new NetworkIdConsistencyValidator.RouteNetworksSpecifiedInMoreThanOneFileNotice(
+            "routes.txt", "route_networks.txt", "network_id");
+    assertThat(notice.toString().equals(expectedNotice.toString()));
+  }
+
+  @Test
+  public void validatesConditionalForbiddenFilePresence2() {
+    networkTableContainer =
+        GtfsNetworkTableContainer.forEntities(
+            ImmutableList.of(new GtfsNetwork.Builder().setNetworkId("network1").build()),
+            noticeContainer);
+    NetworkIdConsistencyValidator validator =
+        new NetworkIdConsistencyValidator(
+            routeTableContainer, routeNetworkTableContainer, networkTableContainer);
+    validator.validate(noticeContainer);
+    assertThat(noticeContainer.getValidationNotices().size() == 1);
+    NetworkIdConsistencyValidator.RouteNetworksSpecifiedInMoreThanOneFileNotice notice =
+        (NetworkIdConsistencyValidator.RouteNetworksSpecifiedInMoreThanOneFileNotice)
+            noticeContainer.getValidationNotices().get(0);
+    NetworkIdConsistencyValidator.RouteNetworksSpecifiedInMoreThanOneFileNotice expectedNotice =
+        new NetworkIdConsistencyValidator.RouteNetworksSpecifiedInMoreThanOneFileNotice(
+            "routes.txt", "networks.txt", "network_id");
+    assertThat(notice.toString().equals(expectedNotice.toString()));
+  }
+}
diff --git a/main/src/test/java/org/mobilitydata/gtfsvalidator/validator/NoticeFieldsTest.java b/main/src/test/java/org/mobilitydata/gtfsvalidator/validator/NoticeFieldsTest.java
index 7877aa1d0f..6ed212c10e 100644
--- a/main/src/test/java/org/mobilitydata/gtfsvalidator/validator/NoticeFieldsTest.java
+++ b/main/src/test/java/org/mobilitydata/gtfsvalidator/validator/NoticeFieldsTest.java
@@ -193,7 +193,9 @@ public void testNoticeClassFieldNames() {
             "validator",
             "value",
             "maxShapeDistanceTraveled",
-            "maxTripDistanceTraveled");
+            "maxTripDistanceTraveled",
+            "fileNameA",
+            "fileNameB");
   }
 
   private static List<String> discoverValidationNoticeFieldNames() {