The Samaritans charity has come under fire over its new partnership with betting company Paddy Power Betfair.
The partnership involves activities such as fundraising, corporate donation and volunteering.
But critics say the charity, aimed at giving support to people in emotional distress or at risk of suicide, is risking its reputation.
Relatives of people who have taken their lives because of gambling addictions say they are "extremely disappointed" with the charity for working with the firm.
John Myers, who lost his son Ryan five years ago when he took his own life aged 27 after becoming addicted to gambling, told the BBC: "They're a charitable organisation so they need to get money from other people, wherever they can. But to throw yourself in with the devil I don't think is right.
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"This industry has destroyed families and destroyed lives.
"To even think about lying in bed with these people is wrong and I think they should rethink it and stop taking their money."
Both organisations say that the Samaritans' insight will help them gain a greater understanding of gambling related harm and, in turn, will help Paddy Power Betfair improve how it helps vulnerable customers.
But Carolyn Harris, chairwoman of the All Party Parliamentary Group on Gambling Related Harm, told the BBC she had concerns about the tie-up.
"At best this is distasteful and at worst it's appalling," she said.
"When you see them [Samaritans] aligning themselves to an industry with a reputation for being responsible for suicides through addiction to gambling - it troubles me.
"For me it legitimises this business. I've met so many people who've lost loved ones, livelihoods and homes through addiction to gambling.
"Everything Samaritans does is to try to solve the problems that all gambling companies have a role to play in creating.
"[Samaritans] should get back to basics and keep doing what's it's been respected for doing for years - its fantastic work."
Yahoo News has contacted the Samaritans for comment.
In February, the chief executive of the NHS said that foreign bookmakers that sponsor Premier League football clubs are failing in their duty to help protect gambling addicts.
Simon Stevens told a conference in Manchester that eight out of nine Premier League clubs sponsored by overseas betting companies have failed to make required donations to an industry charity.
He described gambling addiction as one of the "new threats to public health" and that the Premier League should pressure clubs to pay their dues.