The Professional Pilots Union (PPU) said its members were taking action because Virgin Atlantic was refusing to recognise it and it had been excluded from talks about changes to benefits.
"It’s the last straw; Virgin Atlantic have consistently refused to recognise the PPU as a legitimate and independent union, essentially disenfranchising our members," said the PPU's Steve Johnson.
"Our door is - and has always been - open to Virgin to take the necessary steps to prevent any disruption for Christmas travellers."
The PPU says it represents more than 400 of the airline's pilots while Virgin Atlantic says about 30 percent are members.
"A small number of our pilots have voted for industrial action," Virgin Atlantic said in a statement. "Our absolute priority is to ensure that all of our customers can continue their journeys as planned this Christmas and we’re working hard to protect all of their trips."
The airline's main business is UK-to-U.S. flights. It is owned by Richard Branson's Virgin Group and U.S. airline Delta.
The PPU said it would hold another four-day strikes from Dec. 30 to Jan. 2 and from Jan. 4 to 7.
"We hope that Virgin acknowledge the mandate our members have given us, and help avoid strike action by recognising the PPU and halt the benefits review that is so damaging to our members' long-term security," Johnson said.
(Reporting by Michael Holden; editing by Stephen Addison)