diff --git a/api/src/errors.js b/api/src/errors.js
index 9d94cb0e1c0..390c47e9168 100644
--- a/api/src/errors.js
+++ b/api/src/errors.js
@@ -27,9 +27,13 @@ class AuthenticationError extends Error {
   }
 }
 
+class ReplicationLimitError extends Error {
+}
+
 module.exports = {
   PublicError,
   NotFoundError,
   PermissionError,
   AuthenticationError,
+  ReplicationLimitError
 };
diff --git a/api/src/services/replication/authorization.js b/api/src/services/replication/authorization.js
index b3dad431090..6338ddbc5c1 100644
--- a/api/src/services/replication/authorization.js
+++ b/api/src/services/replication/authorization.js
@@ -8,7 +8,14 @@ const request = require('@medic/couch-request');
 const environment = require('@medic/environment');
 const nouveau = require('@medic/nouveau');
 const { DOC_IDS, PREFIXES, DOC_TYPES } = require('@medic/constants');
+const { ReplicationLimitError } = require('../../errors');
 
+
+const REPLICATION_LIMITS = {
+  SUBJECTS_COUNT: 100 * 1000,
+  SUBJECT_HITS: 500 * 1000,
+  UNPURGED_DOCS_COUNT: 50 * 1000
+};
 const ALL_KEY = '_all'; // key in the docs_by_replication_key view for records everyone can access
 const UNASSIGNED_KEY = '_unassigned'; // key in the docs_by_replication_key view for unassigned records
 const MEDIC_CLIENT_DDOC = '_design/medic-client';
@@ -629,7 +636,7 @@ const getDocsByReplicationKeyNouveau = async (authorizationContext) => {
       uri: `${environment.couchUrl}/_design/medic/_nouveau/docs_by_replication_key`,
       body: {
         q: `key:(${chunk.map(nouveau.escapeKeys).join(' OR ')})`,
-        limit: nouveau.RESULTS_LIMIT,
+        limit: REPLICATION_LIMITS.SUBJECT_HITS,
       }
     });
 
@@ -637,6 +644,17 @@ const getDocsByReplicationKeyNouveau = async (authorizationContext) => {
       continue;
     }
 
+    // A single doc can have multiple hits (for different subjects), so this is not a strict "doc limit", but
+    // it is our "give up" limit
+    if ((hits.length + response.hits) > REPLICATION_LIMITS.SUBJECT_HITS) {
+      authorizationContext.userCtx.replicationLimitExceeded = true;
+      throw new ReplicationLimitError(
+        `User "${authorizationContext.userCtx.name}" exceeds the subject hits limit with at least [${
+          hits.length + response.hits
+        }] subject hits.`,
+      );
+    }
+
     for (const hit of response.hits) {
       hits.push({
         id: hit.id,
@@ -724,6 +742,7 @@ const getViewResults = (doc) => {
 };
 
 module.exports = {
+  REPLICATION_LIMITS,
   DEFAULT_DDOCS,
   updateContext,
   getDefaultDocs,
diff --git a/api/src/services/replication/replication.js b/api/src/services/replication/replication.js
index 26c5d9056e1..10ac3bd737e 100644
--- a/api/src/services/replication/replication.js
+++ b/api/src/services/replication/replication.js
@@ -1,33 +1,63 @@
 const db = require('../../db');
 const authorization = require('./authorization');
+const { REPLICATION_LIMITS } = require('./authorization');
 const purgedDocs = require('./purged-docs');
 const _ = require('lodash');
 const replicationLimitLog = require('./replication-limit-log');
+const dataContext = require('../data-context');
+const config = require('../../config');
+const { users, updateUser } = require('@medic/user-management')(config, db, dataContext);
+const { ReplicationLimitError } = require('../../errors');
+
+const assertUserAllowedToReplicate = async ({ name }) => {
+  const { replication_blocked } = await users.getUserDoc(name);
+  if (replication_blocked === true) {
+    throw new Error(`User "${name}" has been banned from replicating.`);
+  }
+};
 
 const getContext = async (userCtx) => {
+  await assertUserAllowedToReplicate(userCtx);
   const info = await db.medic.info();
   const authContext = await authorization.getAuthorizationContext(userCtx);
   userCtx.subjectsCount = authContext.subjectIds.length;
-  const docsByReplicationKey = await authorization.getDocsByReplicationKey(authContext);
-
-  const allowedIds = authorization.filterAllowedDocIds(authContext, docsByReplicationKey);
-  userCtx.docsCount = allowedIds.length;
-  const unpurgedIds = await purgedDocs.getUnPurgedIds(userCtx, allowedIds);
-  userCtx.unpurgedDocsCount = unpurgedIds.length;
-
-  const excludeTasks = { includeTasks: false };
-  const warnIds = authorization.filterAllowedDocIds(authContext, docsByReplicationKey, excludeTasks);
-  const unpurgedWarnIds = _.intersection(unpurgedIds, warnIds);
-
-  await replicationLimitLog.put(userCtx.name, unpurgedIds.length, allowedIds.length);
-
-  return {
-    docIds: unpurgedIds,
-    warnDocIds: unpurgedWarnIds,
-    warn: unpurgedWarnIds.length >= replicationLimitLog.DOC_IDS_WARN_LIMIT,
-    limit: replicationLimitLog.DOC_IDS_WARN_LIMIT,
-    lastSeq: info.update_seq,
-  };
+  try {
+    if (userCtx.subjectsCount > REPLICATION_LIMITS.SUBJECTS_COUNT) {
+      throw new ReplicationLimitError(
+        `User "${userCtx.name}" exceeds the subject limit with [${userCtx.subjectsCount}] subjects.`
+      );
+    }
+    const docsByReplicationKey = await authorization.getDocsByReplicationKey(authContext);
+
+    const allowedIds = authorization.filterAllowedDocIds(authContext, docsByReplicationKey);
+    userCtx.docsCount = allowedIds.length;
+    const unpurgedIds = await purgedDocs.getUnPurgedIds(userCtx, allowedIds);
+    userCtx.unpurgedDocsCount = unpurgedIds.length;
+    if (userCtx.unpurgedDocsCount > REPLICATION_LIMITS.UNPURGED_DOCS_COUNT) {
+      throw new ReplicationLimitError(
+        `User "${userCtx.name}" exceeds the document replication limit with [${userCtx.unpurgedDocsCount}] documents.`
+      );
+    }
+
+    const excludeTasks = { includeTasks: false };
+    const warnIds = authorization.filterAllowedDocIds(authContext, docsByReplicationKey, excludeTasks);
+    const unpurgedWarnIds = _.intersection(unpurgedIds, warnIds);
+
+    await replicationLimitLog.put(userCtx.name, unpurgedIds.length, allowedIds.length);
+
+    return {
+      docIds: unpurgedIds,
+      warnDocIds: unpurgedWarnIds,
+      warn: unpurgedWarnIds.length >= replicationLimitLog.DOC_IDS_WARN_LIMIT,
+      limit: replicationLimitLog.DOC_IDS_WARN_LIMIT,
+      lastSeq: info.update_seq,
+    };
+  } catch (e) {
+    if (e instanceof ReplicationLimitError) {
+      await updateUser(userCtx.name, { replication_blocked: true }, true);
+    }
+    throw e;
+  }
 };
 
 const getDocIdsRevPairs = async (docIds) => {
diff --git a/shared-libs/user-management/src/users.js b/shared-libs/user-management/src/users.js
index d7d2f413eb5..661140a6617 100644
--- a/shared-libs/user-management/src/users.js
+++ b/shared-libs/user-management/src/users.js
@@ -53,6 +53,7 @@ const USER_EDITABLE_FIELDS = RESTRICTED_USER_EDITABLE_FIELDS.concat([
   'type',
   'roles',
   'oidc_username',
+  'replication_blocked'
 ]);
 
 const RESTRICTED_SETTINGS_EDITABLE_FIELDS = [
@@ -374,6 +375,7 @@ const mapUser = (user, setting, facilities) => {
     external_id: setting.external_id,
     known: user.known,
     oidc_username: user.oidc_username,
+    replication_blocked: user.replication_blocked
   };
 };