The Tigers have been fined $750,000 and had CEO Justin Pascoe provisionally deregistered for not disclosing a $639,000 commitment to club legend Robbie Farah to be an ambassador when he retires.

The $639,000 will be included in the Tigers' 2019 salary cap, placing the club under pressure to shed players from new coach Michael Maguire's playing roster.

"What history tells you is that a salary-cap imposition of more than half a million dollars is a massive imposition on the club and a huge outcome for the way their roster is structured,"' NRL chief Todd Greenberg said.

"I don't have an intimate knowledge of their salary cap. I know they have some space, but it will be a significant issue they'll have to deal with."

It's an issue the Tigers must deal with because "the rules on those types of (ambassadorial) arrangements between clubs and players post-career are absolutely clear," according to the NRL's chief operating officer Nick Weeks.

"They have to be approved by the NRL or they go in a cap.

"So at no time until recently did the club disclose to us an existence of that agreement that was signed in September, 2016.

"After Robbie left, the club paid him money that he was owed under his contract and they approached us to exclude some of those payments on the basis that Robbie was a destabilising influence on the club.

"Now, what they didn't disclose when they made that application was that the club had earlier entered into an ambassador agreement to bring him back (after a one-season stint in 2017 with South Sydney).

"On our assessment of that, that's misleading.'"

The Tigers, though, are privately furious to have been placed in the same boat as Parramatta's systematic salary-cap cheaters of 2016 and plan on commencing legal action against the NRL.

Shell-shocked Tigers chair Marina Go declined to discuss the specifics of their challenge.

But it's understood the joint venture outfit will argue that Pascoe - and the club - were guilty of nothing more than an honest mistake and a simple oversight for not knowing every one of the NRL's complex and extensive salary-cap rules that stretch some 300 pages long.

Pascoe was only two months into the job in 2015 when he agreed to Farah's post-career role, believing it was imperative to rebuild bridges with the club's 2005 premiership-winning hooker to appease fans before he departed in acrimonious fashion for a one-season stint with South Sydney.

The Tigers were paying Farah close to $1 million a season before he left, making the former NSW captain one of the top one per cent of earners in the game - likely more than superstars Johnathan Thurston and Cameron Smith - and insist the notion of needing to offer him more in retirement was absolute nonsense.

"The club derived no advantage from the arrangement," Go said in a statement to AAP.

Australian Associated Press