Unions have attacked the latest tronc guidance from HM Revenue & Customs, branding it unfair to hospitality staff.
The "clarification" released last month by the Revenue appears to indicate that businesses can avoid paying national insurance contributions (NI) by making employees' wages up entirely through tips.
But union representatives fear staff will not have enough overall contributions to be eligible for state benefits and pensions as a result.
Dave Turnbull, regional industrial organiser at the T&G union, said: "It makes a mockery of the minimum wage if the hospitality industry is allowed to use tronc to pay wages and not pay national insurance."
Paul Kenny, GMB general secretary, said: "This could legitimise the theft of money intended by the customer as an additional payment to staff who have served them well."