The move comes after a walkout on Dec. 8-9 forced the cancellation of hundreds of flights and affected thousands of passengers just before the holiday season. TAP usually flies 300 flights a day.
During the December strike, the airline said the two-day action would cost it around 8 million euros ($8.60 million) in revenue.
"Tomorrow we will issue a pre-strike notice of seven days, from 25 to 31 of January," the union said in a statement.
The flag carrier is under an EU-approved 3.2-billion euro bailout plan, which includes the downsizing of its fleet, the cutting of more than 2,900 jobs and the reduction of most workers' wages by up to 25%.
But the cuts have come at a time when surging inflation has left workers struggling with higher costs.
The pace of consumer price growth slowed in December in Portugal but inflation is still near three-decade highs.
($1 = 0.9307 euros)
(Reporting by Patrícia Vicente Rua; Editing by Catarina Demony and Andrew Heavens)
