The IRS backlog of tax returns has swelled over the past year, despite efforts to clear the pileup, according to an agency watchdog.

There were 21.3 million unprocessed paper returns as of May 31, up from 20 million one year prior, the Taxpayer Advocate Service shared in its mid-year report to Congress.

“Unfortunately, at this point the backlog is still crushing the IRS, its employees and, most importantly, taxpayers,” wrote National Taxpayer Advocate Erin Collins, who leads the independent organization within the IRS.