The Republican chairman of a House of Representatives investigatory panel sought documents on Wednesday from the Internal Revenue Service in a battle with the White House over the Democrats' controversial healthcare law.

House Committee on Oversight and Government Reform Chairman Darrell Issa demanded all documents and communications between the IRS and President Barack Obama's White House after the healthcare overhaul law was signed into law in March 2010, in a letter released on Wednesday.

Issa has challenged the Obama administration's authority to administer the healthcare law in states that are refusing to cooperate. A handful of Republican governors have opted not to establish health insurance exchanges that are required by the law.

The IRS is charged with distributing health insurance tax credits through the state exchanges. Issa argues that federally-created exchanges, set up in the resisting states, cannot deliver the tax credits.

At a hearing earlier this month, IRS Commissioner Doug Shulman said the agency can distribute the tax credits.

Shulman acknowledged that "there is some contradictory language" in the health care law.

The oversight committee, which has subpoena powers, requested the IRS documents by September 4. Any weaknesses the committee finds could be used as evidence in a court challenge of the law's implementation.

The Obama administration has refused to turn over to the committee documents it requested from the Justice Department over a botched gun-running operation in Mexico.

That showdown led the House in June to cite Attorney General Eric Holder for contempt.