HM Revenue and Customs has said that it is sending out penalty notices to those employers who have yet to submit annual PAYE returns (P35 and P14s) that were due by 19 May 2009.
The notices began going out on 23 January.
This marks the second round of penalty notices, the first having been issued last September.
The penalty is £100 per 50 employees for each month that a return is outstanding, as from 20 September 2009 to 19 January 2010. This means that an employer with 50 or less employees will receive a £400 penalty.
The penalty is on top of those sent in September 2009.
Employers that have yet to submit their returns are being urged to do so at once.
Firms with 50 or more employees you must file their returns online. Those submitting by paper will be charged a separate penalty for using the wrong filing method.
For the tax year 2009/10 onwards, all employers, whatever the size of their workforce, will need to file electronically.