Daniel Flohr, deputy head of air stewards' union UFO, told public broadcaster ZDF “we could prolong it at short notice” short of concessions from bosses, although “we don't want that”.
A live list on the carrier's website showed 182 flights between major German cities like Berlin, Cologne, Hamburg and Munich were slashed as UFO called members off the job. As of Monday at 1 pm, 60 flights had been cut.
Some connections to cities in neighbouring Austria and Switzerland, including Zurich and Vienna, were also cut.
Set to be folded into Eurowings over the long term, Germanwings operates flights on behalf of the larger Lufthansa subsidiary.
Approximately 15 percent of Germanwings flights will be cancelled or have been cancelled as a result of the strike, a company spokeswoman told the DPA.
“Of the planned 1200 flights during the strike, over 1000 will still be in operation,” said the spokesperson.
With a relatively small number of departures affected, there was little sign of the travel chaos that has accompanied previous broader-based strikes, and many travellers were able to book alternative flights.
Frankfurt airport — Germany's largest — said on its website it was a “normal day” with “occasional short waits at security checks”.
Germanwings bosses judge the strike over rules governing part-time work unjustified.
The labour dispute has already seen a short “warning strike” at four Lufthansa subsidiaries, while the group's flagship airline suffered a two-day walkout affecting 1,500 flights and 200,000 passengers in November.
After failed preliminary talks for an arbitration, UFO called for a strike of Germanwings flight attendants on Friday.
However Ufo warmed that “we fear that three days will not be enough,” said the union in a letter to its members, which was submitted to DPA.