The party said the Government must outlaw fire and rehire.
The party said reports suggest the Government was made aware of the sackings before they were announced, and of the plan to use “exploitative” practices to take on cheaper employees.
The Rail, Maritime and Transport union has claimed that replacement crews are being paid less than the minimum wage.
Shadow transport secretary Louise Haigh has described the sackings as “a line in the sand” ahead of a vote in Parliament demanding the Government outlaws fire and rehire, strengthens workers’ rights, and takes action to force the company to think again.
Labour will call on the Government to suspend contracts with P&O owners DP World until the matter is resolved and remove it from its Transport Advisory Group.
Ms 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.
“On Monday, トーリー MP must join with Labour and vote to ban cruel fire and rehire for good. They must decide which side they are on – loyal workers in Britain or billionaires riding roughshod over rights.”
TUC 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.
“MPs must send a strong signal tomorrow by backing Labour’s motion. Rogue employers need to know they can’t get away with treating workers like disposable labour.”
A Department for Transport spokesperson said: “Ministers and officials have expressed their outrage and frustration at P&O Ferries on their decision and handling of their announcement, and are closely considering the department’s relationship with the company.
“The Transport Secretary has instructed a total examination of any contract in place with P&O Ferries and DP World across Government, and the department is working closely with unions, the Department for Work and Pensions and industry bodies to ensure that workers are supported and signposted to the most relevant support.
“We have serious concerns that their handling may not have followed the correct and legal processes, and strongly urge P&O Ferries to pause the changes announced, and speak with workers to repair the damage caused.”