Seventeen players have been suspended from the PGA Tour, including six-time major champion Phil Mickelson and former world number one Dustin Johnson.

Those players are no longer eligible to play in PGA Tour events - including with sponsors' exemptions.

This prevents those who had resigned their PGA Tour membership from being able to play in tournaments via the back door.

The PGA Tour had denied exemption requests for the first-ever LIV Golf Invitational Series tournament, which began today at Centurion Club not far from London, and commissioner Jay Monahan had previously threatened players with exclusion if they played in LIV events.

"Their participation in the Saudi Golf League/LIV Golf event is in violation of our Tournament Regulations," Monahan wrote in a memo to players today.

"The same fate holds true for any other players who participate in future Saudi Golf League events in violation of our Regulations.

"These players have made their choice for their own financial-based reasons.

"But they can’t demand the same PGA TOUR membership benefits, considerations, opportunities and platform as you. 

"That expectation disrespects you, our fans and our partners."

The move has been branded "vindictive" by LIV Golf, which claimed it "deepens the divide between the Tour and its members".

LIV Golf Investments, the company behind the breakaway series, is majority owned by Saudi Arabia's Public Investment Fund (PIF).

The PIF is Saudi Arabia's sovereign wealth fund and critics say the country is using it for sportswashing.

Monahan notably sought to tie LIV Golf to Saudi Arabia in his memo to PGA Tour players.

Homosexuality is illegal in Saudi Arabia, women's rights are severely restricted, as is free speech, and the country is leading a coalition which has carried out deadly airstrikes across Yemen since 2015.

These issues - plus Saudi Arabia's links to the 9/11 terror attacks - have been at the forefront of criticism over certain golfers' willingness to sign up to the breakaway series, which is made up of 54-hole competitions and will see players compete in teams.

Mickelson previously admitted the project was "sportswashing", claiming the Saudi partners were "scary motherfuckers to get involved with" and "have a horrible record on human rights", as reported by Fire Pit Collective.

However, he defended the breakaway as being in players' best interests as the PGA Tour is "really a dictatorship".

The 51-year-old took a months-long break from golf after those comments were made public, but returned to action today and has been cleared to play at next week's US Open - the lone major he has never won.

Golf's majors are not operated by the PGA Tour.

Fellow Americans DeChambeau and Reed are now poised to join Mickelson in the LIV ranks, and expected to play when the series begins an American swing in Portland on June 30.

DeChambeau was the 2020 US Open champion and Reed, another of golf's most divisive figures, was the 2018 Masters victor.

Neither DeChambeau or Reed, or their representatives, have denied widespread reports they will play in Portland.

As well leading the PGA Tour, Monahan is chair of the International Golf Federation (IGF) Board.

The IGF is golf's International Federation and oversees the Olympic tournament.

For now, LIV events do not offer Official World Golf Ranking (OWGR) points.

The OWGR standings are used to determine Olympic qualification.