Talks aimed at averting strikes by British Airways cabin crew on Christmas Day and Boxing Day were continuing into the night.
Unite leader Len McCluskey and other union officials spent a second day meeting the company under the chairmanship of the conciliation service Acas.
A spokesman said the union continued to pursue progress in the dispute, seeking an improvement on the "poverty pay" of cabin crew employed in the so-called mixed fleet.
BA says it will run a full service on both days even if the strikes by Unite members go ahead.
The talks come as the pre-Christmas bout of industrial unrest rumbles on, with workers who deliver cash to Post Offices striking on Thursday and Friday.
Members of the Communication Workers Union will walk out as part of a campaign against job losses, the closure of a final salary pension scheme and closures.
Union members working in Crown offices were on strike on Monday and Tuesday, and will take action again on Christmas Eve.
Kevin Gilliland, the Post Office's group network and sales director, said the company had contingency plans in place.
He said: "All Post Office branches will be open for business on December 22 and 23.
"We also expect the vast majority of branches to be open on Christmas Eve, although some will close at 12.30pm or during the afternoon in line with their normal Saturday opening hours. All of these branches will close by 4pm."
Meanwhile, a ban on overtime by drivers on Southern Railway continued to cause delays and cancellations to services, which are likely to continue over Christmas.
Members of Aslef went on strike for three days last week, which halted all Southern's services, and are due to stop work for a week from January 9 unless there is a breakthrough in their deadlocked dispute over driver-only trains.
Rail, Maritime and Transport union members on Southern ended their latest 48-hour stoppage at midnight and are set to strike for three days from New Year's Eve over changes to the role of conductors.
Pilots at Virgin Atlantic are due to start a "work to contract" from Friday in a dispute over union recognition.