Jobs could face the axe when P&O reveals plans of its long-awaited ferries review this Tuesday.
P&O has faced competition from budget airlines
As part of the shake-up P&O could cut jobs at Portsmouth, Dover and Calais, where the majority of its ships depart.
Last month P&O said its ferries division moved deeper into the red after competition from budget airlines, other ferry companies and Eurostar.
The ferries review was announced in March and is expected to result in a £50m exceptional-charge cost for P&O.
No-one from P&O was available for comment on Sunday.
Day trips hit
In August chief executive Robert Woods said he was "confident that the ferries review would demonstrate our determination to put that business right".
The number of ferries carrying passengers between the UK and mainland Europe may be cut in a bid to reduce capacity and lower costs.
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.
The company said France's decision to raise duty on tobacco has hit cross-Channel day trips.
However, the situation is much rosier at the group's ports business, which saw an operating profit of £71.4m for the first half.
That helped P&O to more than double operating profits on its ongoing operations to £113.1m.