The charity Samaritans has come in for criticism over its links with the betting company Paddy Power Betfair.
Staff at the group chose Samaritans as their Charity of the Year.
But critics - including relatives of people with gambling problems who took their own lives - say it is risking its reputation by working with the firm.
Both organisations say Samaritans' insight and expertise will help Paddy Power Betfair improve how it helps vulnerable customers.
The partnership involves activities such as fundraising, corporate donation and volunteering.
Samaritans says it will also help it continue its work "to try to reduce the number of deaths by suicide".
But John Myers, who lost his son Ryan five years ago when he took his own life aged 27 after becoming addicted to gambling, said that was not a good enough reason.
"I'm extremely disappointed in the Samaritans.
"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.
"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."
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."
In statements both organisations said the partnership will not just help Samaritans' fundraising efforts, but its insight and expertise will also help Paddy Power Betfair look after vulnerable customers and develop and strengthen its policies in this area.
Paddy Power Betfair added it is "keen to learn from the fantastic work the Samaritans already do, in order to continually improve our responsible gambling tools and interactions".
You can hear more on BBC Radio 4's Money Box programme on Saturday at 12pm or listen again here.