The two frontrunners of the Republican presidential race are threatening to boycott the upcoming CNBC presidential debate if the network doesn’t limit the time for the candidates to be on stage.

In a joint letter to CNBC, Donald Trump and Ben Carson indicated that they would only agree to a 120 minute debate (including commercials) with time for opening and closing statements.

“To be clear, neither of our campaigns agreed to either the length you propose or your ban on opening and closing statements,” the letter read. “In fact, neither of our campaigns were even consulted.”

“Neither of those conditions are acceptable. Neither Mr. Trump or Dr. Carson will participate in your debate if it is longer than 120 minutes including commercials and does not include opening and closing statements,” the signed letter, published by NBC, read.

Earlier today, campaign aides for Donald Trump floated the suggestion that the billionaire presidential candidate might refuse to appear at the upcoming CNBC debate if they don’t specify their criteria.

In an interview with the New York Times, Trump’s campaign manager Corey Lewandowski signaled that Trump was unhappy with the length of the three-hour CNN debate and wanted them to identify the time candidates would be on stage.

“’For us it was imperative that the time be changed to 120 minutes’ for the length of the debate,” he said to the New York Times. “Mr. Trump had been unhappy with the nearly three-hour length of the CNN debate that Republicans recently took part in.”

Lewandowski said that CNBC never discussed the debate criteria but rather sent a memo informing them how it would be.

“The criteria that was outlined by CNBC was never discussed with any of the candidates or the campaigns,” he said. “So what CNBC did was send out a memo and said, ‘Here’s the criteria as you have approved them and that went out to all the campaigns. We said we never agreed to this criteria.’”

Other campaigns have complained about the required polling standards for candidates to participate in the event, particularly Gov. Bobby Jindal.

Speaking to the Times, Lewandowski called for the debate criteria to be laid out in detail for all the candidates.

“Until we have this criteria specifically laid out, it is difficult to participate,” he warned.