Where the employer controverts the right to compensation after notice or knowledge of the injury or death, or after receipt of a written claim, he must give notice thereof, stating the reasons for controverting the right to compensation, using the form prescribed by the Director. Such notice, or answer to the claim, must be filed with the district director within 14 days from the date the employer receives notice or has knowledge of the injury or death. A copy of the notice must also be given to the claimant.