Flight crew at TAP Air Portugal plan four one-day strikes over alleged violations of their work contracts.
The strikes are due to be staged on October 30, November 1, November 30 and December 2, the civil aviation employees union said.
The airline’s claimed violations of contracts “cause a continuous and systematic degradation of work conditions,” news agency AFP reported the union as saying.
It cited the issues of rest time between flights and the right to take at least one weekend off in seven.
A bid to privatise the airline failed in December 2012, and the government is in the process of deciding whether to try again, despite a pilots’ strike in August.
The threatened walkout comes as the airline completed a move of its operations at Heathrow to the new-look Terminal 2.
TAP also plans to raise the frequency of flights between Manchester and Lisbon from seven to 11 a week from the start of the winter schedule on Sunday (October 26).