Moves to ensure that tips are kept by waiters and bar staff have "totally failed", with some employers continuing to profit from extra money left by customers, it has been claimed.
Unite marked the first anniversary of a change in the law by complaining that waiters and waitresses are still not getting fair tips.
The Labour government closed a loophole a year ago under which some employers counted tips towards wages, and launched a voluntary code of practice for the industry.
Unite officer Dave Turnbull said: "Unite has found that one year on from the campaign, there are still too many employers who regard tips as a subsidy for low pay and who see the tips and service charge money left by customers as a pot of cash to which they are free to help themselves.
"Unite members working in restaurants, hotels and bars across the country have seen establishments increase the percentage of service charge they deduct from their pay packets.
"Workers expected their employers to hear the demands of consumers last year to pass all the money they intended for staff to them, but instead many businesses have chosen to continue business as usual and profit from the gratuity charges.
"The Government must now act to implement the review of the tips code that was committed to in order to hold this industry to account. It has been a total failure.
"If the bosses do not do the right thing and pass the tips and service charge money to the waiters and waitresses, then consumers will lose faith in this sector."
Unite will stage a demonstration outside the Business Department in London on Thursday to highlight the complaints.
A Department for Business spokesman said: "The law is clear - tips must not be used to make up the national minimum wage. Enforcers are specifically targeting the hospitality sector, this includes making sure that the new law on tips isn't flouted."