The owner of Royal Mail says the recent wave of strikes at the postal firm have cost it £200m so far.
The dispute with workers in the Communication Workers Union has led to 18 days of walkouts since August.
Royal Mail owner International Distributions Services said the letter and parcels business had lost £295m in the nine months to the end of December.
The firm also said it had been hit by a continued fall in the number of letters being sent and “weaker retail trends”.
The dispute with the Communication Workers Union (CWU) has been going on since the summer, and seven days of strikes in December led Royal Mail to bring forward its last-suggested posting dates for Christmas mail.
The company said that despite last month’s action, “robust contingency planning” meant it delivered more than 110 million parcels and 600 million letters in December.
It also said that up to 12,500 CWU employees returned to work on strike days. Up to 115,000 workers have been involved in the walkouts.
Separately, Royal Mail said the number of people it needed to volunteer for redundancy to meet plans to cut 10,000 posts by August would be “significantly” lower than first expected.
It said the number of voluntary redundancies required would be much less than the 5,000-6,000 initially expected, partly due to employee turnover.