Budget cuts to the IRS are hampering the agency’s efforts to uncover tax cheats, an agency watchdog said last week and more trims are on the way under legislation approved by a GOP-controlled House panel.

IRS budget cuts are hurting tax collections because there are fewer agents chasing delinquent taxpayers, according to a report released Wednesday by the Treasury Inspector General for Tax Administration. The IRS budget has been cut by $1.2 billion since 2010.

The House Appropriations Committee approved IRS cuts of $900 million more on Wednesday on a party-line vote.

Republicans controlling Congress have targeted the much-maligned agency, particularly in the wake of revelations that IRS agents inappropriately singled out tea party groups for additional scrutiny when they sought tax-exempt status.

Enforcement revenue collected by the officers dropped from a high of $3.3 billion in 2012 to $3.0 billion last year, even as the economy improved.

During that time, the number of revenue officers has been cut by nearly a third, to less than 3,000.

“This report dramatically illustrates the long-term effect of IRS budget cuts on the nation’s tax system and revenue stream,” the IRS said in a statement. “Cutting our resources in these areas means hundreds of millions of taxes go uncollected.”

The IRS’ overloaded phone system also hung up on more than 8 million taxpayers this filing season and forced millions more to wait on hold for 30 minutes or longer to get help on their returns. The staffing shortages meant that the IRS was able to answer fewer than 40 percent of taxpayer calls and led to long waits and lines out the door for taxpayers at walk-in centers.