Originally Published: 19 JUL 22 09:21 ET

By Liam Reilly, Wayne Sterling and Ben Church, CNN

(CNN) -- Former US President Donald Trump told golfers that they should join the controversial Saudi-backed LIV Golf Invitational Series and "take the money now," as the breakaway series prepares for its next event at Trump National Golf Bedminster, New Jersey, from July 29-31.

"All of those golfers that remain 'loyal' to the very disloyal PGA, in all of its different forms, will pay a big price when the inevitable MERGER with LIV comes, and you get nothing but a big 'thank you' from PGA officials who are making Millions of Dollars a year," Trump wrote on Truth Social Monday.

"If you don't take the money now, you will get nothing after the merger takes place, and only say how smart the original signees were."

His comments come as families of 9/11 victims urged him to cancel the tournament, citing LIV Golf's Saudi backing, according to a letter sent to Trump Sunday.

The allegations of Saudi government complicity with the attacks on September 11, 2001, have long been the subject of dispute in Washington. Fifteen of the 19 al Qaeda terrorists who hijacked four planes were Saudi nationals, but the Saudi government has denied any involvement in the attacks.

The 9/11 Commission established by Congress said in 2004 that it had found "no evidence that the Saudi government as an institution or senior Saudi officials individually funded" al Qaeda.

Still, the victims' families have pushed for further disclosures, and last year, the FBI released a document that details their work to investigate the alleged logistical support that a Saudi consular official and a suspected Saudi intelligence agent in Los Angeles provided to at least two hijackers.

"The Saudi nation is largely responsible for the death of our loved ones and for the horrific attack on America. And you know it," 9/11 Justice, which represents survivors and family members of the terrorist attacks, said in the letter.

Brett Eagleson is an advocate for the group and his father, John Bruce Eagleson, was among those who died during the World Trade Center attacks. Eagleson told CNN the decision to host the tournament is "unconscionable."

In the letter, he says the decision has caused "deep pain and anger" among constituents, given Saudi Arabia's alleged role in the attacks and material support of al Qaeda, as outlined by FBI reports.

"The FBI notes that much information has come to light since the 9/11 Commission published its report in 2004," Eagleson writes in the letter, "and refers repeatedly to the existence of US-based Saudi 'support networks' for the 9/11 hijackers."

In an email, Eagleson emphasized that the golf course where LIV is slated to play is "in the backyard of where 750 New Jersey residents were murdered."

"The former President correctly speculated in 2016 that Saudi Arabia knocked down the towers and now the FBI has released the documents to prove him right," Eagleson told CNN, "yet he is choosing money over America. So much for America First. A sad day."

The group is requesting to have members visit the former president in the coming days to discuss their concerns and urge him to "cease further business with the regime that was complicit in the murder of our loved ones," according to the letter.

LIV Golf released a statement responding to the letter Monday.

"As we have said all along, these families have our deepest sympathy. While some may not agree, we believe golf is a force for good around the world."

CNN has reached out to representatives for Trump and the Trump National Golf Club in Bedminster for comment.

Notably, last year, the PGA Tour voted to terminate the agreement to play the 2022 PGA Championship at Trump Bedminster. The decision came after the violent attack on the US Capitol by supporters of Trump.

What is LIV Golf?

The tour has held two tournaments so far -- in London and near Portland, Oregon. The circuit's season-ending event is set for late October at Trump National Doral Miami in Florida.

In June, PGA Tour commissioner Jay Monahan announced that all member golfers playing in the controversial Saudi-backed LIV Golf Invitational Series were suspended and would no longer be eligible to participate in PGA Tour tournaments.

The US Justice Department is investigating the PGA Tour over possible antitrust violations involving LIV Golf, the PGA Tour confirmed to CNN last week.

Several top golfers such as Phil Mickelson, Dustin Johnson, Bryson DeChambeau and Brooks Koepka have joined LIV, which is fronted by former world No. 1 Greg Norman and backed by Saudi Arabia's Public Investment Fund (PIF) -- a sovereign wealth fund chaired by Mohammed bin Salman, the Crown Prince of Saudi Arabia.