Labour will tomorrow bid to stage a Commons vote demanding P&O reinstate 800 sacked seafarers.
The ferry line’s decision to fire hundreds of loyal staff without notice triggered a huge public and political backlash.
The move is being investigated to see if the process broke rules.
MPs will use a three-hour debate this evening to lash out at the firm, which runs ships from Dover and Hull.
Labour hopes to force a vote on the outlawing of fire and rehire - and giving P&O’s employees their jobs back.
It wants the Government to “bring forward an urgent bill to strengthen workers’ rights” following the company’s bombshell.
Shadow Transport Secretary Louise Haigh said: “Labour will fight every step of the way for the jobs and livelihoods of these loyal workers.
“This scandalous action must be a line in the sand. If P&O ferries can get away with this, it will give the green light to other exploitative employers.
“It is the consequence of the Tory assault on workers' rights.
“A Labour Government will strengthen employee protections and ban fire and rehire to give people the security they deserve for an honest day's work.”
She urged Conservative MPs to “vote to ban cruel fire and rehire for good”, adding: “They must decide which side they are on - loyal workers in Britain or billionaires riding roughshod over rights."
The motion was backed by the Trades Union Congress.
General secretary Frances O’Grady said: “No matter where their party loyalties lie, MPs should do the right thing and back Labour’s motion to end fire and rehire and demand the immediate reinstatement of all sacked staff.
“Ministers have spent the last few days condemning P&O’s actions – now they have a chance to prove they mean it.
“P&O ferries and its owner DP World have acted without shame, we can’t let them off the hook.
“No ifs, no buts. MPs must send a strong signal by backing Labour’s motion.
“Rogue employers need to know they can’t get away with treating workers like disposable labour.”
Chancellor Rishi Sunak lashed out at P&O’s “appalling” decision to fire the sailors.
He told BBC1’s Sunday Morning show: “What we are seeing is appalling, the way they have treated their workers is awful, it’s wrong.
“Across government, we are examining not just those actions and whether they comply with the regulations as they should have done, but also our own relationship with the company.”
