Castleford fan Alison Grey posted on social media during the game in Perpignan that she was initially asked to take down a flag she had displayed in support of LGBTQ rights for “health and safety” reasons.
Grey tweeted: “Just been told I am not allowed this flag because the club does not allow it. How disgusting.”
In a later interview with Sky Sports, she added: “We were asked if we could take the flag down, first because it was against health and safety. When we said that there were other flags around the ground they gave up.
“They then came back to us later on and said it was against the views of the club to have the flags.”
Grey did not say whether she did take the flag down.
The Super League is investigating the matter, the organization said in a statement, and will have more details by Monday.
“Rainbow flags are not banned at our club. It is not forbidden,” Catalans Dragons said in a statement, according to PA Media.
“We are gathering more information about what happened,” the club said.
A devout Christian who has made 73 international appearances for Australia in rugby union, Folau signed a one-year deal with the Dragons last month to return to the 13-man code.
Folau, 30, reached a settlement with Rugby Australia last year after being sacked for an Instagram post in which he said “hell awaits” gay people.
At the time of Folau’s signing, the Rugby Football League — the sport’s governing body — said allowing the signing had been a “difficult decision” and deplored the player’s previous comments.