Union’s general secretary Mick Lynch said the demonstration will take place at the offices of Clyde Marine Recruitment, Govan Road, on Monday from 11am.
On Saturday, the union’s Scottish leader Gordon Martin hinted at the protest taking place when he addressed the Alba Party spring conference in Glasgow.
Mr Martin publicly accused the recruitment firm of hiring staff to replace the almost 800 sacked seafarers.
Clyde Marine Recruitment has said it had no prior knowledge about the mass sacking on Thursday last week.
A number of demonstrations have already taken place at ports around the UK amid calls for P&O Ferries’ chief executive Peter Hebblethwaite to resign over the company’s decision to use agency staff on cheaper salaries, including on the Cairnryan-Larne line between Scotland and Northern Ireland.
Speaking ahead of Monday’s protest, Mr Lynch said: “We are making it clear that there is nowhere to run and nowhere to hide for those who have been complicit in the P&O jobs massacre.
“We will keep the pressure on at every opportunity until we get justice for the P&O workers
“We look forward to another good turnout tomorrow after the weekends protests and greatly appreciate the remarkable solidarity from our trade union colleagues in this dispute.
“There will be more protests, more campaigning and more political pressure this week as we ratchet up the fight and harness the public anger at the jobs carved up on our ferries.”