The newly appointed head of the Internal Revenue Service had gotten off to a good start with lawmakers when he took the job in May, but Daniel Werfel has since angered Republicans who say he's failed to turn over 98 percent of the documents they requested as part of their investigations into tax agency practices.

House Oversight and Government Reform Committee Chairman Darrell Issa, R-Calif., wrote to Werfel, the acting commissioner, accusing him of trying to “delay, frustrate, impede, and obstruct the Committee’s investigation.”

Issa threatened to begin issuing subpoenas if he doesn't receive the information he requested.

Issa’s panel is looking into an inspector general’s report that the IRS singled out conservative groups seeking tax exempt status for special scrutiny and delay.

Issa said he received less than 2 percent of the relevant documents needed by committee to complete its investigation. The 2 percent amounts to about 12,000 pages, according to Issa’s letter, but much of the paperwork is heavily redacted. Issa said the pages are blacked out to excess, going far beyond what is needed “to protect confidential taxpayer information.”

Issa said the IRS is also refusing to turn over the results of its own internal investigation into the targeting.

Werfel has appeared several times before House and Senate panels to discuss problems facing the IRS. In addition to the targeting, the agency has spent lavishly on employee conferences and promised millions in bonuses to employees.

The agency also continued paying some top IRS employees placed on forced leave for their roles in the targeting.

Lawmakers have grown increasingly frustrated with Werfel at committee hearings, though he has also been praised by both Republicans and Democrats for his efforts to reform the agency.