Strike action is set to hit five main Oxfordshire post offices on Christmas Eve, in a row over opening hours.

About 50 members of the Communication Workers' Union will walk out at 12.30pm, claiming that is the time they traditionally stop work for the Christmas break.

But Royal Mail managers want them to stay until 4pm to give people more time to collect pensions and child benefits for the four-day holiday.

The sites affected are known as Crown offices because they are owned by Post Office Ltd and the staff are employed by the Royal Mail.

The offices are St Aldate's, in Oxford city centre, Upper Bar, Cowley, High Street, Abingdon, High Street, Banbury, and Market Square, Witney. Managers will fill in for counter staff during the walkout.

Sub-post offices, which are privately run, will not be affected by the action and will open until 4pm as usual.

The Post Office is urging people wanting to collect benefits before Christmas to either go in the morning or visit a smaller office.

David Mills, chief executive of the Post Office, said: "The call for strike action is unnecessary and unjustified.

"Around two million customers, who rely solely on the Post Office for access to their cash, are dependent on our network being open on Christmas Eve so that they can obtain their benefit payments and have cash over the following four-day Christmas holiday.

"The elderly and the disabled are among the groups which most rely on the Post Office. We're determined to do everything possible to ensure our customers can visit our branches until 4pm on Christmas Eve."

Mr Mills said it was "entirely reasonable" to expect staff to work a full day, or most of it, on Christmas Eve, as they were paid until the end of their scheduled duty.

CWU national officer Andy Furey said: "The Post Office's position is both intransigent and illogical. There's no need to keep offices open until 4pm on Christmas Eve and to suggest otherwise is absurd.

"Our members work tirelessly in the run-up to Christmas to provide an excellent service, and to try to force them to work at a time when they want to be with their family and friends is insulting. What sort of festive message is that?

"The 12.30pm finish has been in place for decades. The public are used to it and employees deserve it.

"We have exhausted every single avenue to avoid industrial action, but the Post Office's dogmatic stance has left the union with no other option."

Kevin Duffy, of the Oxford branch of the CWU, said: "We're supporting the staff involved -- most other Post Office workers finish at 12.30pm, but not them."