diff --git a/.rubocop_todo.yml b/.rubocop_todo.yml
index 8fa3ab5..2c014bb 100644
--- a/.rubocop_todo.yml
+++ b/.rubocop_todo.yml
@@ -1,6 +1,6 @@
 # This configuration was generated by
 # `rubocop --auto-gen-config`
-# on 2024-03-29 19:02:54 UTC using RuboCop version 1.56.2.
+# on 2024-03-29 19:48:59 UTC using RuboCop version 1.56.2.
 # The point is for the user to remove these configuration records
 # one by one as the offenses are removed from the code base.
 # Note that changes in the inspected code, or installation of new
@@ -10,14 +10,19 @@
 # Configuration parameters: AllowedParentClasses.
 Lint/MissingSuper:
   Exclude:
-    - 'app/services/time_off_creator.rb'
+    - 'app/services/time_off_builder.rb'
 
-# Offense count: 8
+# Offense count: 9
 # Configuration parameters: AllowedMethods, AllowedPatterns, CountRepeatedAttributes.
 Metrics/AbcSize:
   Max: 34
 
-# Offense count: 12
+# Offense count: 1
+# Configuration parameters: AllowedMethods, AllowedPatterns.
+Metrics/CyclomaticComplexity:
+  Max: 8
+
+# Offense count: 13
 # Configuration parameters: CountComments, CountAsOne, AllowedMethods, AllowedPatterns.
 Metrics/MethodLength:
   Max: 23
@@ -31,9 +36,9 @@ Style/OptionalBooleanParameter:
     - 'app/models/maintenance_contract_model.rb'
     - 'app/utils/analytics/finances/models/financial_statements_of_work.rb'
 
-# Offense count: 8
+# Offense count: 10
 # This cop supports safe autocorrection (--autocorrect).
 # Configuration parameters: AllowHeredoc, AllowURI, URISchemes, IgnoreCopDirectives, AllowedPatterns.
 # URISchemes: http, https
 Layout/LineLength:
-  Max: 124
+  Max: 130
diff --git a/app/controllers/time_offs_controller.rb b/app/controllers/time_offs_controller.rb
index 8942cd7..89f772b 100644
--- a/app/controllers/time_offs_controller.rb
+++ b/app/controllers/time_offs_controller.rb
@@ -15,10 +15,10 @@ def create
     msg = success ? { id: time_off&.id } : 'The time of request creation failed'
 
     render json: msg, status: success ? :ok : :unprocessable_entity
-    rescue StandardError => e
-      logger.fatal "Error: TimeOffCreator: #{e.message}, Params: #{time_off_params}"
-    
-      render json: { message: e.message }, status: :internal_server_error
+  rescue StandardError => e
+    logger.fatal "Error: TimeOffCreator: #{e.message}, Params: #{time_off_params}"
+
+    render json: { message: e.message }, status: :internal_server_error
   end
 
   def destroy
diff --git a/app/models/time_entry.rb b/app/models/time_entry.rb
index d6da173..16ba22c 100644
--- a/app/models/time_entry.rb
+++ b/app/models/time_entry.rb
@@ -31,6 +31,20 @@ class TimeEntry < ApplicationRecord
   validates :date, presence: true
 
   validates :date, uniqueness: { scope: %i[user_id statement_of_work_id] }
+  validate :assignment_must_exist_in_period
 
   scope :active_in_period, ->(start_date, end_date) { where('date <= ? AND date >= ?', end_date, start_date) }
+
+  def assignment_must_exist_in_period
+    assignment_exists = Assignment.joins(:requirement)
+                                  .where(user_id:)
+                                  .where(requirements: { statement_of_work_id: })
+                                  .exists?(['? >= assignments.start_date AND ? <= assignments.end_date', date, date])
+
+    # If not, add an error.
+    return if assignment_exists
+
+    errors.add(:base,
+               'There is no valid assignment for the user and statement of work in this period.')
+  end
 end
diff --git a/spec/models/time_entry_spec.rb b/spec/models/time_entry_spec.rb
index 7abb2ed..fa90c0b 100644
--- a/spec/models/time_entry_spec.rb
+++ b/spec/models/time_entry_spec.rb
@@ -35,4 +35,25 @@
     it { should belong_to(:statement_of_work) }
     it { should belong_to(:user) }
   end
+
+  context 'assignments' do
+    it 'is valid if there is an assignment active for the sow' do
+      start_date = Time.zone.today - 1.day
+      end_date = Time.zone.today + 1.day
+
+      assignment = create(:assignment, start_date:, end_date:)
+      sow_id = assignment.requirement.statement_of_work.id
+      time_entry = TimeEntry.new(date: Time.zone.today, hours: 8, statement_of_work_id: sow_id, user_id: assignment.user.id)
+
+      expect(time_entry).to be_valid
+    end
+
+    it 'is invalid if there is no assignment active for the sow' do
+      user = create(:user)
+      sow = create(:statement_of_work)
+      time_entry = TimeEntry.new(date: Time.zone.today, hours: 8, statement_of_work_id: sow.id, user_id: user.id)
+
+      expect(time_entry).not_to be_valid
+    end
+  end
 end