Treasury Department officials are refusing to give congressional Republicans information on how they developed the legal basis for giving Obamacare subsidies to people enrolled in federal health insurance exchanges.

“A lot of the discussion was oral in meetings, in-person discussions, but to the extent that there are additional documents that may relate to internal deliberations,” Deputy Assistant Secretary for Tax Policy Emily McMahon told Rep. James Lankford, R-Okla., during a House hearing, “we have concerns about confidentiality and the chilling effect that release of those additional documents might present on the rule-making process if we were to provide them.”

McMahon also noted that Treasury allowed House investigators to review two legal memoranda pertaining to the proposed rule and final rule on the exchange subsidies, though they could not have copies of the memos because the briefing was in camera.

The question of whether the federal government may subsidize federal exchanges will likely be settled by the Supreme Court.

“The statute provides subsidies for certain individuals who buy insurance on a state-established exchange but not on a federally-facilitated exchange,” Attorney General Scott Puritt, R-Okla., said in his prepared statement to the House Oversight Subcommittee on Health Care, on the panel that preceded McMahon’s testimony.

“The State of Oklahoma’s decision—as well as decisions by 34 other states—not to establish an exchange should have prevented substantial federal spending as well as significant compliance costs both for the states as employers and for private employers,” Pruitt added.

Rep. Matt Cartwright, D-Penn., suggested during the hearing that the federal government has never provided a tax credit to some Americans, but not others, based on what state they live in.

McMahon also said that the Treasury Department took into account the likelihood that Congress intended for the subsidies to go to all exchanges.

“We recognized that would have been a very different approach that was contemplated by the Affordable Care Act,” she said. “We appreciated that it would have been a very significant difference.”