P&O has faced competition from budget airlines

The company could lose up to 1,000 workers in Dover and Portsmouth, as it struggles to compete with budget airlines and Eurotunnel.

On Monday, the Rail Maritime and Transport Union (RMT) criticised a "lack of consultation", saying it would not tolerate compulsory redundancies.

The announcement from P&O is due to be held on Tuesday morning.

We will draw a line in the sand at compulsory job losses Bob Crow RMT

Losses at P&O's ferry arm for the six months to 30 June were �25.1m, compared to �19.9m a year earlier, while revenues were down to �467.1m from �505.7m.

Officials from the RMT have been called to a meeting with the company in Dover on Tuesday.

Its general secretary, Bob Crow, complained the company had not consulted properly with its workforce.

"We found out that we were being consulted over the possibility of job cuts when we read about it in the media.

"It is no use consulting us after a decision has been taken. We need meaningful consultations before any announcement is made.

"We are happy to talk about efficiencies but we remain opposed to redundancies and we will draw a line in the sand at compulsory job losses."

The union says P&O was one of the ship companies which had benefited from the tonnage tax which had cost the taxpayer more than �100m.