Research by the union found nearly a fifth of employees have been told by their employer that they’re not allowed to discuss their pay with co-workers.

TUC general secretary, Frances O’Grady, said pay secrecy clauses are “a get out of jail free card” for bad bosses.

“They stop workers from challenging unfair pay, allow top executives to hoard profits and encourage discrimination against women and disabled people,” she said.

“Talking about pay can feel a bit uncomfortable, but more openness about wages is essential to building fairer workplaces.”

According to the research, more than half (53%) of workers are not given information about other people’s pay in their organisation.

And fewer than one in five (18%) report that their workplace has a transparent pay policy, where salary details are available to everyone through an official source.