Talks between British Airways and union leaders aimed at averting a cabin crew strike were brought to an abrupt end when protesters stormed the meeting.
Dozens of demonstrators from the Socialist Workers Party breached security at the London offices of a conciliation service.
The two sides negotiated for more than five hours on Saturday before the protesters interrupted the meeting, and it is not known whether progress was made.
The planned cabin crew strikes follow a long-running dispute over jobs, pay and working conditions.
More than 100 demonstrators gathered outside the building, and a number pushed past security to reach the 23rd floor office. Unite union leader Tony Woodley remonstrated them, telling them to "shut up".
BA cabin crew, who are Unite members, are set to begin a five-day strike on Monday, with more strikes to follow from 30 May and 5 June.
Earlier, British Airways reported its biggest annual loss due to lower passenger numbers, higher costs and the impact of strike action.
The airline lost Stg 531 million in the 12 months to March - the biggest loss since it was privatised in 1987.
