Gambling firms may face a compulsory levy to help problem gamblers
Two-thirds of gambling companies have failed to contribute anything to a fund for supporting problem gamblers, the BBC has learned.
Only 1,000 of 3,200 licensed gambling firms have donated money, says the Responsibility in Gambling Trust.
The trust has reached its target of £3.6m in voluntary donations - but says many firms have not given anything.
The culture secretary has previously said the government may introduce a compulsory levy.
The money is used to treat problem gamblers and to fund research into gambling addiction.
This year, the trust has raised £100,000 more than the original £3.5m target.
But the trust says the money came mainly from the larger companies, such as the big high street betting firms and casino operators.
This means the majority of smaller licensed gambling operators, including casinos, bookies, bingo halls and gambling websites, gave nothing.
RIGT chairman John Greenway says all it can do is write to companies to remind them of their responsibilities.
"We sent around 3,200 letters twice, but all we have available to us are the names and addresses of operators. We don't have the information about what they do or how big they are," he said.
The Gambling Commission review will be published in Autumn
Despite this, Mr Greenway remains optimistic about reaching their target of £7m in voluntary contributions by 2010.
"I think we can, but I think those parts of the industry which have been most generous to us want to make sure they're not subsidising non-payers."
But Ian Semell from the Gambling Therapy website doubts that extra money can be raised using current methods - and he thinks there is a need for much more funding.
"Perhaps they need to have somebody out there actively campaigning and getting to know the people that run these companies, and using a salesman technique to go out there and actually ask people for money.
"Because at the end of the day, if they don't contribute, I'm sure there will be an enforced levy," he said.
Successive culture secretaries have threatened a compulsory levy if the industry does not contribute more.
Most recently, Andy Burnham said in February that he was surprised by the low level of donations - at that point only 360 firms had contributed.
He said it was not acceptable, and asked the industry to deliver a substantial increase in contributions or face a statutory levy.
Liberal Democrat culture spokesman Don Foster told BBC Radio 5 Live that problem gambling was "a major and growing problem".
He said the amount contributed was about £14 per problem gambler in the UK, compared with £44 in New Zealand and £40 in Canada.
"It's the online gamblers on the whole who are not contributing," Mr Foster said. "It's difficult to get money out of these people - some of them are operating from overseas.
"We've got to say once and for all, 'Here is the amount we want - £7m plus, in a couple of years'.
"Let's use that as the threat to the industry. Cough up double what's being paid now or else we have a compulsory levy to raise that amount of money."
The Gambling Commission is currently reviewing the effectiveness and level of the current voluntary arrangements for the gambling industry's funding for gambling research, treatment and public education.
Its findings, due to be published this autumn, will be taken into account by the Department of Culture, Media and Sport and will affect the likelihood of a compulsory levy.
You can hear more on Radio 5 Live Breakfast on Saturday 26 April, 0600 BST to 0900 BST.