About 5,000 members of the Verdi services union started walkouts on Monday to press for an immediate 9.8 per cent pay rise. Lufthansa had offered 6.7 per cent over 21 months and a one-off payment.
Lufthansa shares were trading 0.95 per cent higher at €14.91 (Dh85) by 0803 GMT, outperforming Germany's DAX blue-chip index, which was down 0.64 per cent.
Lufthansa has grounded planes because of a shortage of technical staff. Catering and freight workers and some check-in staff have also downed tools.
Some analysts estimated the walkouts could cost the company €5 million ($7.79 million; Dh28.5 million) per day and on Wednesday, the group said soaring fuel costs and a possible weakening in demand were set to push earnings down this year.
Europe's biggest economy is experiencing a sharp rise in inflation and several unions are seeking bigger wage deals after restraint in recent years.
Lufthansa usually runs about 2,000 flights per day.