AAP understands Greenberg contacted his counterpart on Friday after it emerged Wallabies coach Cheika had a one-on-one conversation with Ponga to enquire about his desire to switch codes at some point in his career.

Cheika on Friday was defiant, saying he was acting in the best interests of the 15-man game, however the episode had been received poorly at Rugby League Headquarters.

Greenberg and the NRL are of the belief that there should be a handshake agreement not to attempt to steal each other's talent while they still have several years to run on their contracts.

The Queensland fullback's Newcastle deal runs out at the end of 2021 and he has an option in his favour for another year.

And just as rival NRL clubs cannot negotiate with Ponga and his management until the final season of his contract, Greenberg hopes RA will be similarly respectful.

Greenberg and Knights CEO Phil Gardner issued a strongly worded statement in which they issued a hands-off edict.

"Kalyn is a wonderful talent and a fine ambassador for rugby league and the Knights, and it is not surprising that there would be interest in him at the appropriate time," Greenberg said.

"The nature of this interest is certainly unorthodox.

"Kalyn has a significant period remaining on his contract and it would be disappointing to see any contact made to any player under these circumstances."

Ponga played rugby union at the prestigious Anglican Church Grammar School in Brisbane during his teens and had spoken of his admiration of the All Blacks, describing them as the "pinnacle".

He spent part of his childhood in New Zealand and All Blacks coach Steve Hansen had previously expressed his interest in Ponga.

A frustrated Gardner admonished Cheika and described his conduct as inappropriate.

"It's not surprising that rugby union have identified Kalyn as a talent they wish to get their hands on," Gardner said.

"What does come as a surprise is that an official from their code would personally phone our talent despite the fact he has several seasons left to run on his contract.

"It is inappropriate for any contact to be made from rugby union - or anyone else for that matter - and it is extremely disappointing.

"The reality is Kalyn is under contract for another two-and-a-half years with the option for a third year.

"I can assure not only Knights supporters, but fans of the game, we will be doing everything in our power to sign Kalyn long term when the time is right."

Australian Associated Press