House Republicans are escalating their scrutiny of the decision to delay a key part of the health care overhaul, questioning whether the Obama administration even has the authority to "ignore the law" without the approval of Congress.

The administration announced early last week that it was delaying by one year a requirement that large employers offer access to health insurance. Officials described the delay as a common-sense concession to businesses who complained the rules were too onerous, and maintained the Treasury Department was within its right.

A Treasury official told FoxNews.com that the move was "an exercise of the administrative authority" under the IRS code. The official said the department has "longstanding" authority to "grant transition relief when implementing new legislation" like the health care law.

A number of Republicans pointed to the sudden change as a sign of problems to come with the massive health care law. But, as lawmakers return on Monday from the holiday break, they're also challenging whether the tweak was an abuse of power.

"This action raises a lot of questions about whether the Obama administration can simply ignore the law when it's convenient for them," Rep. Phil Roe, R-Tenn., said in a statement.

He said he's asked the Congressional Research Service to "investigate" that issue -- "because I don't think any president has the authority to pick and choose what parts of law to follow."

The matter will get an airing on Capitol Hill later this week. Rep. Kevin Brady, R-Texas, chairman of a House Ways and Means subcommittee, has set a hearing for July 10 which, in part, will examine the issue of the administration's authority to change the law.

Rep. Darrell Issa, R-Calif., chairman of the House Oversight and Government Reform Committee, went a step further, describing the move as "another in a string of extra legal actions taken" by the Obama administration.

The complaint about the administration's authority is just one of several Republicans have regarding the move to delay the mandate. They question whether more delays and changes are in store in the run-up to the Jan. 1 launch of many of the law's major provisions. They question why the so-called individual mandate -- the requirement on individuals to buy health insurance -- wasn't also delayed.

But the Treasury Department and White House, in announcing the delay last week, explained that they did so after businesses complained about the reporting requirements. As the administration moves to simplify the rules, they said, they would in turn give businesses more time to comply.

"We have heard concerns about the complexity of the requirements and the need for more time to implement them effectively. We recognize that the vast majority of businesses that will need to do this reporting already provide health insurance to their workers, and we want to make sure it is easy for others to do so," Mark J. Mazur, the assistant secretary for Tax Policy at the Department of the Treasury, said last week on the Treasury blog.