A SHOWDOWN is looming between clubs and the NRL over a controversial proposal to increase the salary cap by $150,000 a season but abolish third-party agreements for marquee players.

In a move certain to be challenged at the next chief executive's conference on March 6, salary cap auditor Ian Schubert wants to scrap the system which has helped clubs to retain some of their biggest players through outside payments from sponsors.

Instead, it is planned to allow clubs to spend an additional $150,000 on player payments - a move those whose players have third-party sponsorship deals claim unfairly penalises them, while others say they don't have any extra money to meet a salary cap increase to $4.25 million.

The Roosters, Rabbitohs, Dragons, Broncos and Cowboys are the clubs most likely to be affected by any change, with Willie Mason, Craig Wing, Mark Gasnier, Darren Lockyer and Johnathan Thurston among the players with third-party deals.

Under the proposal, those arrangements would be included in the salary cap, whereas other clubs which haven't been as proactive can spend up to $150,000 more on recruiting and retaining players.

But NRL chief executive David Gallop last night described third-party agreements as the most difficult area of the salary cap to police, while he said the clubs were not on a level playing field as some did not have wealthy sponsors able to top up the contracts of star players.

"At this stage we have circulated a discussion paper only but the clear fact is that third-party agreements and third-party payments by sponsors to players is the most problematic area of the salary cap," Gallop said.

"There are examples of clubs guaranteeing players a third-party agreement when they sign, which on any view is tantamount to a payment by the club that should be included in the cap.

"One problem area is determining just how much work should a player do to be a genuine payment rather than simply part of a sponsors relationship with the club, which means that clubs with ready access to sponsors can get an advantage in terms of the salary cap.

"But we are simply seeking feedback on whether clubs want to continue with this arrangement and we will then assess it."

Clubs have been asked to respond to the proposal by February 28 ahead of the CEO's conference in Sydney on March 6, the day of the season launch at Birchgrove Oval.

Schubert's interpretation of some third-party agreements, which he considers on a case by case basis, has angered some clubs in the past and there was vigorous debate on the issue before the number of marquee players able to earn up to $50,000 extra was increased last year from two to three.

Those clubs that want the system retained argue that it is bringing additional money from outside the game to increase player payments. "We have always supported the third-party sponsorship agreements as being in the best interests of the game, the sponsors and the players," St George Illawarra chief executive Peter Doust said.

Wests Tigers chief executive Steve Noyce, whose club was forced to pay a $50,000 fine after breaching the salary cap over a third-party agreement last year, welcomed the changes. "[The third-party sponsorships] cause everyone a bit of angst," he said. "Some clubs have more trouble finding them. So when we talk about a level playing field … I just think they're a difficult animal. They're tough to obtain and they're tough to police.

"Rules and regulations that get everyone off-side are not what the game's about."

Penrith general manager Mick Leary admitted his club had never utilised the third-party arrangement. "We've never had one," he said. "It's very difficult in this area. Souths and the Roosters, maybe Manly, wouldn't have any trouble - that's not being derogatory, I'm just saying good luck to them. They're in the top end of town where they can market their product."

Warriors chief executive Wayne Scurrah said none of his club's players had third-party agreements but was opposed to any salary cap increase. "We are the club most affected by the National Youth Competition as we now have a second team to fund so we don't have another $150,000 to spend," he said.