WASHINGTON—A federal judge has rejected a request from the IRS to allow new regulations on hundreds of thousands of tax preparers to take effect while the issue is decided on appeal.

U.S. District Judge James Boasberg ruled last month that the IRS exceeded its authority by imposing a series of new regulations on tax preparers. The rules would require tax preparers who are not attorneys or certified public accountants to pass a competency exam and take annual continuing-education courses.

The IRS says the rules are needed to address a growing problem of poorly filed returns. Three independent tax preparers sued to block the regulations, saying they were onerous and put them at a competitive disadvantage.

On Friday, Boasberg rejected an IRS request to delay his ruling pending a likely appeal.