"If you want to go somewhere on vacation and have it ruined for you, it's not OK. They should sit down and come to an agreement," Lufthansa passenger Elfriede Bretagne told Reuters TV in Frankfurt, at Germany's busiest airport.

Industrial action in the dispute has already wiped 160 million euros ($200 million) off Lufthansa's operating profit, adding to pressure from a stuttering global economy and increased competition.

The carrier lowered its profit guidance for 2015 for a second time this October, and is expanding budget brand Germanwings to better compete with the likes of Ryanair and easyJet.

Lufthansa's supervisory board is due to approve plans for the Germanwings expansion at a meeting this week.

Goodbody analyst Mark Simpson said further walk outs in the coming weeks could be even more damaging.

"We see any strike threats in the immediate run up to the busy Christmas period as representing an even more significant risk than those scheduled for today and tomorrow," he said.

At 1500 GMT, Lufthansa shares were down 0.3 percent at 14.31 euros.

The Germany-wide strike is to last from midday (1100 GMT) on Monday to 1159 pm (2259 GMT) on Tuesday for short- and medium-haul flights, as well as from 3 am (0200 GMT) to 1159 pm (2259 GMT) on Tuesday for long-haul flights.

Pilots flying for Lufthansa Cargo will strike from 3 am to 1159 pm on Tuesday. Germanwings flights are not affected.