Ironically, the same lawmakers pressing the lawsuit on Thursday actually voted on legislation that would have delayed the mandate a year ago. But pushing that through the Democratic-controlled Senate would have required debate, possibly other changes, and a likely delay just as the administration was gearing up to put the measure into practice.

Justifying the apparent contradiction of suing the President over taking action they actually supported initially, Republican aides said it is up to Congress to make those changes in law, not the President.

Not personal

Another centerpiece of the initiative required individual Americans to obtain health insurance from Obamacare or on the private market, or face a possible fine. So far 9 million people have signed up for plans under the health law, the administration has said.

It's the signature domestic policy achievement of Obama's presidency so far and a rallying cry for Republicans, especially on the midterm campaign trail.

Earlier in the day, Boehner argued a suit wasn't simply a personal issue, but a move to defend Congress as an equal branch of government.

"It's not about Republicans versus Democrats. This is about the legislative branch that's being disadvantaged by the executive branch. And it's not about executive actions. Every president does executive orders," Boehner said.

Saying most presidents act lawfully, Boehner said Obama "is basically rewriting law to make it fit his own needs."