The Internal Revenue Service says 100,000 paid tax preparers who worked on 2011 returns did not follow new rules requiring them to register with the agency.

The IRS launched an initiative last year to better police a largely unregulated industry used by most taxpayers. All paid tax preparers must get an identification number from the IRS and to provide it on returns they prepare. They will eventually have to pass a competency exam and get annual training.

The agency said it is sending letters to 100,000 preparers who signed 2011 returns but did not provide proper identification numbers.

Some 712,000 tax preparers have registered so far. The rules do not apply to certified public accountants, lawyers or enrolled agents because they already are regulated through their professions.