The Deregulation Task Force said legislation brought in following the Lyme Bay accident in which four youngsters died was an "ill-conceived" reaction to the tragedy.
It claimed the prosecution and subsequent imprisonment of those responsible was the most effective way of reducing the possibility of a similar accident.
And it said the Health and Safety Executive's own cost-benefit analysis for the new licensing regime for outdoor activity centres showed improved safety was likely to be minimal and would be heavily outweighed by its cost.
The Task Force - mainly industrialists - claimed many centres would be unable to afford inspection and licensing fees of up to Pounds 1,400, and would go out of business.
"The effect will be that enjoyable and beneficial outdoor activities will in future be denied to many youngsters, especially the less well off, without any comparable improvement in safety for those who can still participate."
In its second annual report, the Task Force urged the Government to postpone the licensing regime pending a study of the costs and benefits of the Act, with the possibility of it being repealed.
"At the least the Government should review the effect of this Act after two years with a view to repeal at that time," it said.
Ministers rejected the call, but said they were committed to a thorough review in three years. They said it was premature to suspend arrangements before then.
David Jamieson, the Labour MP whose private member's Bill became the Act, said the Task Force was out of step with what parents, teachers and the industry wanted.
"They just look at the bottom line of the account sheet and the safety of our young people doesn't matter at all," he said.
Alan Parker, education officer with the Association of Metropolitan Authorities, said: "The Deregulation Task Force appears to be arguing that it's OK if a few children get killed every now and again, provided those responsible are prosecuted as a result and this will discipline everybody to behave properly. This is monstrous."
Local authorities wanted outdoor activity centres to be covered by an "OFSTED model" of inspection rather than the regulatory approach adopted by the HSE.
Mr Parker said: "This would focus on ensuring that any provider would have to employ only properly-trained and qualified staff in respect of the services they offered."