Trump reveals conservative group calling him 'worst kind of politician' asked him for $1 million
Donald Trump during an interview on Aug. 20, 2015. (CNN)

Republican presidential candidate Donald Trump's squabble with the conservative Club for Growth advocacy group escalated on Sunday when he produced a letter purportedly showing the organization asking him for a $1 million donation.

According to Newsmax, Trump posted a picture of the document online on Sunday, while denouncing the group as a "mafia organization of extortion." The post can be seen below:

The photo came five days after Trump accused the club of becoming "nasty" toward him when he refused to give them the money during a meeting. The group then accused the real estate magnate of requesting the meeting.

"Thought he could buy us off," the club stated. "Worst Kind of Politician."

The club also highlighted a 2011 column pointing out that Trump had defined himself as "liberal" on health care, and did so again after Trump posted the letter:

As Politico reported, the club has promised to bundle contributions to the campaigns of fellow Republican candidates Jeb Bush, Ted Cruz, Rand Paul, Marco Rubio and Scott Walker.