Donald Trump and Ben Carson are both threatening to boycott the next Republican presidential debate if CNBC, who is hosting the event, and the Republican National Committee do not change the stated format of the event.

“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 letter, obtained exclusively by NBC News and signed by both candidates, reads.

The @GOP should not agree to the ridiculous debate terms that @CNBC is asking unless there is a major benefit to the party. — Donald J. Trump (@realDonaldTrump) October 15, 2015

They take issue with CNBC's plans for a debate that doesn’t include opening and closing statements, and runs two hours plus up to another 16 minutes in commercial breaks. According to Politico, CNBC distributed a memo outlining these plans that indicated all candidates had agreed to them.

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In the letter, the candidates write that “neither of our campaigns agreed to either the length you propose or your ban on opening or closing statements. In fact, neither of our campaigns were even consulted.”

According to the New York Times, aides to a number of candidates expressed concerns with the debate parameters during a Wednesday conference call with the RNC and CNBC. In an interview with the Times, Trump Campaign Manager Corey Lewandowski threatened to skip the debate if the criteria aren't changed.

But the letter, addressed to CNBC Washington Bureau Chief Matthew Cuddy, puts that threat to paper. In it, the campaign says that “neither” the refusal to include opening and closing statements, nor the potentially extended time frame, “are acceptable.”

"Both our campaigns hope that you will agree with these very reasonable format changes so that CNBC may present all the Republican candidates to your audience,” the candidates write.

In response, Brian Steel, a spokesman for CNBC, suggested the network may budge on its criteria, promising to “take the candidates’ views on the format into consideration” going forward.

"Our goal is to host the most substantive debate. Our practice in the past has been to forego opening statements to quickly address the critical issues that matter most to the American people. We started a dialogue yesterday with all of the campaigns involved and we will certainly take the candidates’ views on the format into consideration as we finalize the debate structure,” Steel said in a statement.