The Internal Revenue Service is acknowledging that the agency spent tens of millions of dollars in recent years on conferences for thousands of its employees.

Details of the conferences are expected to appear in a report set for release Tuesday by the Treasury Department watchdog that also confirmed allegations that agency officials had improperly targeted certain political groups seeking tax-exempt status.

The forthcoming report focuses especially on an August 2010 conference held in Anaheim, Calif., for roughly 2,600 agency employees in the IRS’s small business and self-employed division, a unit that assists small business owners with tax preparation and is based in Lanham.