House Republicans on Friday accused Treasury Secretary Jacob Lew of obstructing their investigation into the IRS’s targeting of tea party and conservative groups, and issued subpoenas for more agency documents.

Oversight committee chairman Darrell Issa, California Republican, sent a scathing latter to Mr. Lew blasting him and President Obama for dismissing the GOP’s claims about IRS targeting as a “phony” scandal, saying that Mr. Lew has “attempted to thwart” his investigation.

“Over two months since the committee first requested documents, the IRS has produced only a small fraction of responsive documents,” Mr. Issa said.

The IRS is an agency within the Treasury Department.

Mr. Issa said he’s willing to work with the agency to tailor his requests for information, but he said the IRS has unilaterally decided to revise the scope of its search of documents. The committee had asked for 81 search terms to be used to identify responsive documents, but the IRS cut that to 12, he said.