The United States will be plunged in a “constitutional crisis” if President Obama takes unilateral action to delay deportations, Rep. Steve King (R-Iowa) said Thursday.

King, a leading opponent of the immigration bill passed by the Senate last year, sounded the alarm about reports that Obama is planning large-scale action to defer deportation for millions of illegal immigrants, perhaps as soon as next week.

“This president has been floating the trial balloon on executive amnesty for a long time," King said. “Today, new details surfaced that the president plans to attempt amnesty as early as next Friday, sending us into a constitutional crisis." 

King noted that Obama has previously said he did not have the authority to suspend deportations by executive order.

"The audacity of this president to think he can completely destroy the rule of law with the stroke of a pen is unfathomable to me," King said. "It is unconstitutional, it is cynical, and it violates the will of the American people.

Speaker John BoehnerJohn Andrew BoehnerRestoring fiscal sanity requires bipartisan courage GOP congressman slams primary rival for Ryan donations Speculation swirls about Kevin McCarthy’s future MORE (R-Ohio) and incoming Republican Senate Leader Mitch McConnellAddison (Mitch) Mitchell McConnellLawmakers feel pressure on guns Bipartisan group of House lawmakers urge action on Export-Import Bank nominees Curbelo Dem rival lashes out over immigration failure MORE (Ky.) have both issued strong warnings that Obama should not act on his own.

"I’ve been very disturbed about the way the president has proceeded in the wake of the election," McConnell said Thursday.

Both leaders are facing growing calls from Republicans to block Obama's actions through the spending bill that must be passed to avoid a government shutdown in December.

King said Congress must use the "power of the purse" to protect its constitutional role.

"This is about defending our oath to the Constitution too. We cannot allow Barack ObamaBarack Hussein ObamaOvernight Energy: Dems ask Pruitt to justify first-class travel | Obama EPA chief says reg rollback won't stand | Ex-adviser expects Trump to eventually rejoin Paris accord Overnight Regulation: Trump to take steps to ban bump stocks | Trump eases rules on insurance sold outside of ObamaCare | FCC to officially rescind net neutrality Thursday | Obama EPA chief: Reg rollback won't stand Ex-US ambassador: Mueller is the one who is tough on Russia MORE’s anticipated, unconstitutional act to be implemented, for if it is it will destroy the pillars of American exceptionalism. Come what may, we must always protect the Constitution.”