An email from Raelene Castle to her fellow club CEOs is threatening to expose the simmering tension at Belmore between the Bulldogs boss and her chairman, Ray Dib.

Castle, who is one of four CEOs on the salary cap advisory committee, sent an email to all club bosses on Thursday morning, asking them to sign a letter of complaint against the Rugby League Players' Association for breaching negotiation protocols by meeting with a select group of chairmen on Monday.

However, Fairfax Media understands the email has not gone down well in some quarters, notably with the New Zealander's own chairman, Dib, who helped organise the meeting with the RLPA on Monday.

The letter, written by the NRL's salary cap negotiator Dean Kino to the RLPA and sent as an attachment by Castle, reads: "We are equally disappointed by your consequent conduct on the 9th of May, 2017, in holding a meeting with certain NRL club chairpersons for the express purpose once again of providing and negotiating your position with respect to the 2018 to 2022 CBA."

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Dib wasn't aware the email was being sent out and, according to rival club bosses, wasn't impressed when learning of his CEO's email on Thursday morning.

While some described it as the beginning of a feud between the pair, it is understood Castle told people she wasn't having a shot at her boss, rather taking aim at the RLPA for breaching the agreed protocols in relation to privacy and confidentiality.

The email was expected to be the topic of great conjecture on Thursday night when club powerbrokers gathered at ANZ Stadium before the round 10 clash against the Cowboys for a monthly board meeting.

There has long been a suggestion Castle and Dib haven't seen eye to eye on certain issues, including the recent protracted contract negotiations surrounding coach Des Hasler.

It has also recently been reported that Castle was unaware of private discussions between Dib and Kieran Foran's representatives to lure the five-eighth from the Warriors to Canterbury next season.

But Castle's perceived indiscretion over the email, however inadvertent, threatens to bring the disagreements to the fore and a backroom brawl seems inevitable at Belmore.

There can be little doubt that the protracted salary cap dispute between the NRL and the RLPA has contributed to the angst in clubland, with clubs recruiting players without knowing what their spending limitations will be next year.

At Belmore, the signings of Foran and Aaron Woods have already put enormous pressure on the club's roster for 2018, while the lucrative four-year deal for James Tedesco at the Roosters has also left the tri-colours lobbying for an increased cap beyond $9 million.

That is why Roosters boss Nick Politis and Dib are understood to have called the meeting with the RLPA last week, joined by Scott Penn (Manly), Dave O'Neill (Penrith), Nick Pappas (Rabbitohs) and Allan Hawke (Raiders).

Castle is on the NRL salary cap advisory committee alongside Don Furner (Canberra CEO), Jim Doyle (Warriors CEO) and Paul White (Brisbane CEO).

Interestingly, Furner signed the letter of complaint to the RLPA despite his chairman attending the meeting with the RLPA on Monday.

Also in the letter was a reference to a breach of protocol when the RLPA sent out information about the proposed salary cap position to coaches and media on Friday, despite an agreement to keep matters confidential.