Everton have been sponsored by a car company for two seasons after previously ending a gambling sponsor deal early
More than 20,000 people have signed an online petition calling for Everton to drop their new gambling sponsor.
The club announced the "record" deal with online casino stake.com two weeks ago, meaning logos will appear on men's and women's team shirts next season.
But there has been criticism from fans, with campaigners calling the move "saddening".
Everton have previously said betting sponsors are "not ideal" but needed to consider commercial decisions.
Many fans have accepted the club needed to take a different path after posting £372m in losses over the last three seasons, and it is understood there are no plans to ditch the new partnership.
But the recorded level of opposition to a sponsor is believed to be unprecedented in English football.
Norwich also ditched a gambling sponsor last season after fans protested about sexualised marketing material, while Preston North End did not renew their betting partnership after they said they took fans view into consideration.
Everton season ticket holder Ben Melvin, who has "suffered with gambling addiction for many years", said he set up the petition because he wanted to send a message to the club about what he believes are "harmful products".
Melvin, who has written to Everton, said: "The partnership does not sit right with the club's motto, the standards the club sets off the pitch and the fantastic work done by the club's Everton In The Community in tackling mental health issues.
"I didn't anticipate the petition to get to the level it has, and I realise Everton may not change their decision, but I want them to know how many people have signed it and understand how some fans feel."
A recent YouGov survey reported 1.4 million people in Britain were being harmed by gambling with a further 1.5 million at risk.
But the Premier League, the English Football League and Betting and Gaming Council all say there is no evidence to show a causal link between gambling sponsorship and problem gambling.
The government is set to decide on whether to change gambling laws, including a ban of sponsorship in football, next month.
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