The Rugby Football League have fined Castleford £40,000 after the Tigers were found guilty of misconduct.
Sections of the Castleford support directed homophobic chanting at Crusaders' dual-code winger Gareth Thomas in the Super League fixture between the two at the Jungle on March 26.
Thomas, who announced he was gay in December, joined Crusaders in March and the Castleford game was his second for the club.
A statement from the RFL read: "Castleford were found guilty of unacceptable behaviour, of breaching the RFL's Respect Policy, of misconduct by their supporters and of conduct prejudicial to the interests of the sport.
"The tribunal was chaired by his Honour Judge Rodney Grant, who criticised the club for failing to take steps to stop the homophobic chanting, for failing to identify the perpetrators, for failing to challenge the chanting and for their failure to undertake a meaningful inquiry afterwards."
The Tigers, who must pay £20,000 immediately with the other half suspended until the end of 2011, have also been ordered to forfeit the £20,000 suspended from the £40,000 they were fined last year after bottles were thrown on to the pitch and officials were threatened following a game with Catalans.
Castleford have already signalled their intent to appeal the decision, with chief executive Richard Wright claiming to be "shocked" by the verdict of the tribunal.
"To say we are disappointed and shocked is an understatement," he said.
"The evidence does not support the decision and does not in any way support the scale of the penalty. We totally refute the outcome of the hearing."
Rod Findlay, who has been advising the company on behalf of sports law specialists McDaniel and Co, added: "There was some chanting on the day, we agreed this with the Tribunal panel, there were three incidents lasting only a few moments, two of which were drowned out by public address announcements.
"The club condemns any person who makes or chants obscene remarks towards players or officials. But the charges against the club are not that there was chanting, they are that the club failed to take its' best endeavours to prevent or stop any chanting.
"This the club refutes totally. The club has a well-established system for dealing with chanting and could not have done any more on the day."
Castleford have 15 days to formally lodge their appeal.
