Unions fear some restaurants and other businesses may slip through the net of new legislation over the fair distribution of tips and service charges that comes into force in Great Britain on Tuesday.

The government said the long-planned changes would mean workers would be in line for about £200m that may otherwise have been retained by employers.

Under the new rules 100% of tips – by cash or card – and any service charge levied on customers must be passed on to staff working in restaurants, cafes, hotels, hairdressers or taxi firms.

The minister for employment rights, Justin Madders, said: “When you tip someone for good service, you expect them to keep all their tip. They did the work – they deserve the reward.

“This is just the first step of many in protecting workers and placing them at the heart of our economy. We will be introducing further measures on tipping to ensure workers get their fair share of tips.”

However, the Unite union said some waiting staff would remain out of pocket, including workers in Northern Ireland where legislation has yet to be introduced by the Stormont executive.

Neil Moore, the union’s lead regional officer for hospitality in Northern Ireland, said: “Stormont’s failure to implement fair tips legislation has left bosses free to dip their hand in the tips when it suits them.”

Bryan Simpson, the lead organiser for hospitality workers at Unite, added: “Unite has campaigned for this legislation for over a decade so we welcome its belated introduction as it will make a massive difference to millions of hospitality workers. However, there are still national employers out there who have already brought in policies that will see workers lose out of tips.”

He pointed to Miller & Carter, the steakhouse chain owned by the nationwide pub group Mitchells & Butlers, which the Guardian last year revealed was taking payments from waiting staff in some restaurants worth up to 2% of the sales they serve up.

The payments are intended as a way for waiting staff to share tips with chefs and other back-of-house workers.

But Unite claims the system can sometimes lead to earnings from tips and service charges being less than the amount owed to fellow workers.

A spokesperson for Mitchells & Butlers said it passed on all tips to staff: “In preparation for the new tips code of practice, our tipping policies were reviewed by an independent professional adviser to ensure that we remain fully compliant.

“Our approach under the new tips code of practice remains that our teams will agree how to distribute tips in each business through a democratic and transparent process, facilitated by each onsite general manager.”

It said distribution of tips was “entirely up to our individual teams in each of our [businesses].”