Sir Keir Starmer said there would be “no watering down” of the Labour party’s new deal for working people.

“I’m absolutely committed to our new deal for working people,” he said after a meeting of Labour’s mayors at GTG Training in Wolverhampton.

Sir Keir said: “This will be the biggest levelling up of workers’ rights in a generation, so there will be no watering down.”

Under the deal, the party plans to empower adult social care professionals and trade unions that represent them to negotiate a sector-wide agreement for pay, terms and conditions.

The Labour leader said: “I think people should always be treated with dignity and respect at work but I also think it’s essential for economic growth, because every good employer knows that to get better economic growth we need to treat our workforce properly.”

The plan presents “no threat” to employers, he said, adding that “good employers are doing much of this already”.

“So no watering down, 100% committed to it – and it is about respect and dignity but it’s also a story about economic growth and taking our country forward,” he said.

In early May, Labour faced a backlash from unions after the Financial Times reported the party was going to announce that all policies in its “new deal” for workers will go through a formal consultation process with businesses, which could delay or tone them down.

Unite general secretary Sharon Graham warned at the time that “a red line will be crossed” if the party U-turns on previous employment pledges while TUC president Matt Wrack said any weakening of policy would draw a “hostile reaction”.

Labour defended its plan on Sunday after a report from the Policy Exchange think tank that said that party’s fair pay agreements could cost taxpayers £4.2 billion a year.

A Labour Party spokesperson said those claims were “based on fiction”.

The calculation was based on an assumption that the sector-wide minimum wage was set at £15 per hour, and that Labour would follow a model used in New Zealand.