Hull KR chairman Neil Hudgell is leading a campaign against the signing of Israel Folau by Catalans Dragons.
Sky Sports News has confirmed the story first reported by BBC Sport that an email has been sent to the French club warning them of the consequences, should Hull KR suffer financial losses as a result of sponsors or commercial partners walking away from the sport.
The French club have been widely criticised following the announcement that they had signed the dual-code international, who was sacked by Rugby Australia last May for anti-LGBT+ social media posts.
Several other clubs are now understood to be supporting Hudgell's stance, with many of them unhappy about the amount of notice they were given before the signing was announced.
Super League club chiefs will meet at Salford on Wednesday, with the signing of Folau top of the agenda. Catalans Chairman Bernard Gausch is expected to make a rare appearance, as he usually sends a representative.
Catalans ignored the warnings of both the Rugby Football League and Super League with their signing of the 30-year-old Folau on a one-year contract but the transfer has been defended by the club's chairman Bernard Guasch and head coach Steve McNamara.
Speaking on Tuesday, McNamara said: "We knew it would be controversial. As an individual I stand by the club's statement that Bernard issued. I fully support that statement.
"An opportunity arose when an overseas player left our club, we needed an outside back. We looked in France, England and overseas.
"We went down the route of investigating a fair few players. Israel was on that list, and having spent a lot of time speaking to him and understanding him a lot more, and getting the reassurances we did, we made a decision as a club that we would support the signing of Israel and give him another opportunity in our game."
'Every chance' Folau could make debut versus Wakefield
Folau trained with his new team-mates for the first time on Tuesday, and could be in line to make his debut at Wakefield on Sunday, according to Sky Sports News reporter Fraser Dainton.
"The big question is when he will make his debut for the Dragons. When I was in France at the time the news was announced last week, it was 50-50 in terms of French fans who were either happy or unhappy with him joining the Catalans.
"The Australian has proved to be a divisive figure among supporters we spoke to at the Stade Gilbert Brutus on Saturday.
"While some were happy for such a high-quality player to be joining club - provided he keeps his religious views to himself - others were concerned his arrival will damage the image and values of Catalans and the sport as a whole.
"Perpignan's LGBT66+, which represents over a hundred and fifty LGBT members - are dismayed, and are concerned that work they have done to foster relations between various different sports groups will be damaged.
"The Dragons are scheduled to play Wakefield Trinity at the weekend but given the fact he hasn't played a game of rugby for at least nine months and he hasn't featured in a rugby league game for several years, his involvement will probably be minimal.
"There is every chance he may come off the bench for the last 10 minutes, given the fact he is training from Tuesday.
"He will get a good few sessions with his new team-mates and have time to get a grasp of what head coach Steve McNamara wants from him.
"McNamara did say to me after their season-opening game against Huddersfield Giants that the Dragons are particularly short in Folau's position (centre). So the possibility remains that he could potentially feature this weekend."