Donald Trump is expected to sign a GOP loyalty pledge, vowing not to launch a third-party bid if he does not win the Republican presidential nomination in the general election next year.

So far, Trump is the only one out of the 17 GOP candidates running in the 2016 presidential race that has admitted that he would consider running as either an independent or third-party candidate. However, the Republican National Committee said that it is asking all of the contenders to sign the pledge.

According to GOP sources, the loyalty pledge states: "I affirm that if I do not win the 2016 Republican nomination for president of the United States I will endorse the 2016 Republican presidential nominee regardless of who it is. I further pledge that I will not seek to run as an independent or write-in candidate nor will I seek or accept the nomination for president of any other party," reports ABC News.

Sources say that the GOP frontrunner will sign the pledge sometime on Thursday, reports the Washington Post.

Last month, the billionaire businessman refused to promise to back the party's nominee at the during the first primetime GOP debate on Fox News.

If the real estate mogul was to make an outside bid, then he would potentially hurt the Republican candidate's chance of getting enough votes to beat the Democratic candidate.

As a result, RNC officials have been actively trying to sway Trump's campaign not make a third party run in order to avert such a scenario.

Several candidates have already confirmed that they would sign the pledge, including Ohio Gov. John Kasich, former Florida Gov. Jeb Bush and New Jersey Gov. Chris Christie.

"Every candidate has to make the decision about do you really want the nomination of our party or do you want to have it both ways," Christie told Fox News on Thursday, according to The Chicago Tribune.

"I've made my decision. I want the nomination of our party and I'll support whoever the nominee is if it's not me. That's the decision Donald has to make."