Her comments come after Wests Tigers chairman Lee Hagipantelis said any NRL players who don't get vaccinated could have their contracts torn up.

Fagan, who wasn't speaking on behalf of the Raiders but as a lawyer, said there were so many different circumstances that could arise it would be hard for the NRL to make a blanket decision when it came to mandatory vaccination.

She felt each case would need to be judged on their own circumstances.

Two NBL players have already parted ways with their clubs after refusing to get vaccinated - American Travis Trice (Illawarra Hawks) and Tai Webster (NZ Breakers) - with international travel further complicating matters.

Vaccination for COVID-19's likely to become necessary to be able to travel internationally and domestically, which meant any unvaccinated NRL players might not be able to travel for away games.

Raiders prop Josh Papalii has already said he won't be getting vaccinated on medical grounds, while Joe Tapine was another member of the Green Machine who got an exemption from getting an influenza shot on medical grounds.

"Most employers have the ability to make a lawful and reasonable direction, so the employee can't refuse to comply with that, but the onus is on the employer to show it is lawful and reasonable," Fagan told The Canberra Times.

"It's complicated and it absolutely turns on the circumstances of each case ... There's so many different circumstances it's hard to make a blanket decision."

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Fagan said the onus would be on an employer or government to show any vaccination mandate was reasonable.

She said the Fair Work Commission had already said it may be reasonable to do so in certain circumstances.

"Say there's a public health order in NSW or Queensland that said to enter a football stadium you had to be vaccinated or gain an exemption - that would make it impossible to do your job unless you were vaccinated," she said.

"But by the same token you can't discriminate against people.

"If someone has a health condition and if the government can't show it's reasonable to mandate that that makes it difficult.

"In the end it might be a court that decides whether it was a lawful and reasonable direction."

Hagipantelis said NRL players might be unable to fulfill their contractual obligations as employees if they didn't get vaccinated.

The Brydens Lawyers principal was also the major sponsor of the NBL's Sydney Kings and was currently dealing with the vaccination debate within the NBL.

Hagipantelis said if players didn't get vaccinated then it could constitute a reason to terminate their contract because they might not be able to travel interstate or overseas.

"These organisations, the NRL and basketball, are employers of players who have a contractual relationship with the organisation to provide a particular service,'' Hagipantelis told SEN Radio.

"That service, as provided for in the contract, would include interstate and international travel.

"The fact that they would be unable to fulfil their contractual obligations by reason of their choice not to get vaccinated means that the contract is frustrated and perfectly entitled for the employers to terminate.

"Will that occur in the NRL? I'm absolutely convinced it will." with AAP.