The British Broadcasting Corporation News.
The P&O Ferries crew in Dover are being paid less than the Indian crew, according to the union.
The low pay was a betrayal of those who have been sacked, according to the Rail, Maritime and Transport union.
A close source said the figure was "wholly inaccurate" and that P&O wouldn't comment on agency workers' pay.
The minimum wage in the UK is set by law, but some of P&O's ferries are registered in Cyprus.
Firms using UK ports can register their ships in other countries and pay lower wages.
The minimum wage in the UK is $8.89 per hour. A spokesman for P&O said safety was the top priority and the new crewing management model was used by many competitors.
There were protests outside the London offices of P&O on Monday.
Mick Lynch said that P&O staff were being replaced by exploited workers.
We don't have any beef with those people. He said that they want those people to be paid the wages that they have negotiated for.
The union is calling for a boycott of P&O services and wants the Government to look at legal options to get the workers back.
Ferries are expected to start sailing again on Monday.
The services were stopped after P&O announced in a video call that 800 staff were being sacked.
journeys will remain suspended for the next few days according to the company. The sailings between Dublin and Liverpool have resumed.
They have recruited high-quality experienced seafarers, who will now be familiar with the ships, going through all mandatory training requirements set out by our regulators.
A barrier system will be put in place to manage any disruption caused by P&O freight when the M20 is closed between junctions 8 and 9.
When the motorway reopens on Tuesday, the coastbound section will be used by Eurotunnel and other goods vehicles, but it will be queueing if necessary.
All other traffic should follow the signs and cross over to enter the M20 London bound motorway.