The politician is urging people to join the latest blockade at the Cairnryan terminal on Friday against the ferry firm’s recent sacking of dozens of workers at the port.
Mr Smyth will be taking part in the blockade, organised by the Rail, Maritime and Transport Workers Union (RMT), at 2pm which comes just days after P&O Ferries resumed crossings to Larne.
The Prime Minister pledged to force the firm to reverse its decision to sack workers including those at Cairnryan.
Boris Johnson told Westminster “P&O plainly are not going to get away with it", but so far workers remain out of a job and have been replaced by agency workers .
Mr Smyth said: "I am once again urging local people to consider supporting the latest blockade, because the sacked P&O workers need our support more than ever. We must show P&O bosses that we won’t let this go.
“The ferries are now running again and yet there has still been no meaningful action against them from the UK Government, just hot air from Boris Johnson and a Secretary of State for Scotland Alister Jack who had been posted missing.
“Both the UK and Scottish Governments promised to review the tens of millions of pounds of contracts they have with P&O Ferries, but again they have failed to do so, and this inaction has meant workers have had no choice but to sign up for their redundancy payments or risk losing them.”
It has been reported that all but one employee has accepted the Dubai-based firm’s payoff.
Mr Smyth continued: "Even if our Governments have given up the fight, I know workers haven't and I'd urge the local community to join us at the blockade to highlight their solidarity. I'm also calling on local Tory politicians to come out of hiding and show their support.
“Without stronger action from the UK Government, P&O Ferries will be let off the hook.
"That will be devastating for those loyal workers kicked out of their jobs, bad news for the local economy and a green light to bad bosses up and down the country to treat staff like disposable labour. We can't let that happen!"