Boris Johnson has been accused of letting P&O bosses off the hook after they illegally sacked 800 seafarers.
The Prime Minister had pledged to force the firm to reverse its decision and reinstate sacked workers.
He told MPs: “P&O plainly are not going to get away with it.”
But in spite of a criminal investigation launched by the Government’s Insolvency Service, replacement crews will be kept on – with their wages as low as £5.50 an hour.
Get all the latest news sent to your inbox. Sign up for the free Mirror newsletter
A spokesman for Nautilus, the union representing a third of the sacked workers, said: “P&O has got away with it. There’s no fine, there’s only words and hot air.”
Ministers passed responsibility to the Insolvency Service, the agency which deals with redundancies, but it has not set a timetable for the investigation.
TUC general Secretary Frances O’Grady said: “Without stronger action from the Government, there’s a real risk P&O will be let off the hook. And that would be a green light to bad bosses up and down the country to treat staff like disposable labour.
“This investigation by the Insolvency Service must not shy away from serious sanctions and big financial penalties. Firms who behave like corporate gangsters deserve far more than a slap on the wrist.”
Rival DFDS warns it cannot compete unless P&O’s move is blocked, raising fears for hundreds more seafaring jobs.
Ms O’Grady demanded a halt to contracts on proposed freeports in which P&O’s owner DP World has a £50million stake until crews are reinstated. But all but one of the sacked crew has now either accepted or opened talks on termination deals worth around £15,000.