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 BoehnerA warning to Ryan’s successor: The Speakership is no cakewalk With Ryan out, let’s blow up the process for selecting the next Speaker Race for Republican Speaker rare chance to unify party for election MORE (R-Ohio) and incoming Republican Senate Leader Mitch McConnellAddison (Mitch) Mitchell McConnellRepublicans divided over legislation protecting Mueller The Hill's Morning Report: Inside the Comey memos Democrats mull audacious play to block Pompeo 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 ObamaPaltry wage gains, rising deficits two key tax reform concerns Throwing some cold water on all of the Korean summit optimism Colorado state lawmakers advance measure to rename highway after Obama 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.”