The workers' union says Fortnum & Mason's tipping policy has become 'shrouded in secrecy' since it introduced a new tronc system in July and claims that staff have been told to accept a cut in pay to the National Living Wage of £7.20 an hour to get a share of the 12.5 per cent service charge.
It says the fact that the tronc system is run by an external company goes against its advice to restaurant operators to have a transparent scheme which is 'run by staff for staff'.
Unite regional officer Dave Turnbull said: “Fortnum & Mason bosses are treating its loyal and hardworking staff with utter contempt. It needs to start operating a fair, clear and transparent policy to show how it distributes its 12.5 per cent service charge or risk alienating staff and customers alike.
“We believe that diners will be outraged to learn that the 12.5 per cent service charge they have just paid is being controlled entirely by an outside consultant without any input from staff or clear information on how much of the fee it is pocketing for itself."
However, a statement from Fortnum & Mason stated that the company had consulted with staff to implement a 'new, dynamic and fair tronc system' in July and there had been no complaints.
"Nothing was imposed: staff were given a proposal to consider on an individual basis, and of our 250 hospitality staff, only one opted out, who remains with the company," it said.
"The devising and administration of a Tronc system is by its very nature complicated, and to ensure operation within both the letter and spirit of the law, Fortnum's engaged a respected independent company, WMT Troncmaster Services Ltd, who continue to manage the arrangements.
"Since the new Tronc system, which is in line with industry standards, came into being, Fortnum's has not had a single complaint from staff. The 20 hospitality staff at the company's outlet at Heathrow T5 were not included in the 2015 consultation because it was a new site without an established trading record. The company has commenced a consultation with the hospitality staff at T5. This is ongoing."
Unite has held protests at a number of hospitality businesses over tipping practices. In February it protested outside STK London over claims that the restaurant's service charge was being used to bolster the wages of senior managers and in 2015 it held a protest outside PizzaExpress.
“We remind the Government of the huge public outcry sparked by the last tipping scandal and urge it to get a move on with publishing the recommendations of its consultation into tipping which closed on 27 June this year," said Turnbull.
“It’s simply inexcusable that there remains a stubborn core of unethical employers willing to use tips and service charges for their own enrichment, when others in the casual dining sector have taken positive steps to adopt fairer and more transparent tipping policies."