RMT general secretary Mick Lynch said: “Due to the pressure from RMT seafarers, P&O have been prevented from further cutting the pay of vulnerable agency crew.
“There are no depths to which P&O and their Dubai owners at DP world will sink to extract the maximum profit from ferry crews operating our vital maritime supply chains.
“This is underlined by the fact that despite this U-turn, P&O are still only paying barely half of the UK minimum wage of £9.50 per hour.
“Ultimately, staffing ships with super-exploited agency staff is not just morally wrong, it undercuts those remaining ferry operators who do abide by union rates of pay and conditions and undermines passenger safety.
“The only way out of this latest crisis at the ferry operator is for the government to take over the running of P&O vessels and reinstate directly employed staff on union rates of pay. “
RMT also went on to refute P&O claims they did not ask agency workers to accept lower rates of pay.
A union spokesman said: "P&O's statement is contradictory. On the one hand, they claim there was an "administrative misunderstanding" which they rectified. And on the other they say there was never an attempt to pay agency workers lower rates of pay.
"The fact is P&O were caught trying to pay people from South America inferior wages to their counterparts in Europe and the MCA made them change those contracts.
"We have seen contracts of agency workers where they are being paid the equivalent of £4.35 an hour for 17 weeks work. This is less than half the current UK national minimum wage."