Lufthansa was forced to cancel more than 200 flights and delay many more at Frankfurt Airport, Germany's busiest, following a strike by the Independent Flight Attendants Organization, or UFO, that lasted from 5:00 a.m. to 1:00 p.m. local time on Friday.

Lufthansa said it "sincerely regrets" that the labor dispute came with a short notice and, thus, created additional problems for passengers. The carrier, Europe's largest by passenger numbers, said it was forced to cancel the majority of flights in and out of Frankfurt, particularly short- and medium-haul flights. Long-haul flights to U.S. cities, Tel Aviv and Chennai, India, were also canceled.

Lufthansa Regional and Germanwings flights were not affected by the strike.

The carrier said Friday that when the strike finishes, "delays must be anticipated."

"Even after the end of the strike, Lufthansa foresees irregularities in flight operations from and to Frankfurt," it said in a statement. "Lufthansa regrets any inconvenience to its passengers caused by the strike measures and will do its utmost best to minimize the impacts."

About 1,000 staff, or 90 percent of UFO members, stopped working at 5:00 a.m., stranding thousands of passengers at Frankfurt's main terminal building. Lufthansa's crew reportedly handed out juice and water to people stuck waiting in long lines.

The UFO union said Thursday that it seeks 5 percent pay raises for the airline's more than 18,000 cabin crew. It called the strike after 13 months of negotiations for higher pay and guarantees that its members would not have to accept cheaper contracts with the carrier's partner budget airlines failed to reach an agreement. Lufthansa has offered 3.5 percent and is trying to cut approximately €1.5 billion ($1.9 billion) from its costs by the beginning of 2015.

Nicoley Baublies, head of the UFO union, told the German radio station Bayerischer Rundfunk it could just be the beginning if Lufthansa does not match its demands.

"It depends on how Lufthansa responds now and how much they try to break the strike and put our people under pressure," Baublies said, claiming the union would decide Friday evening whether to stage another strike Saturday and expand to more airports.

"That's always possible, and we will announce it with six hours' notice," he said.

The strike at Frankfurt Airport, Europe's third-busiest, had a spill-over effect on other airlines. The airport ran short on parking spots due to the grounded Lufthansa planes and had to halt all Frankfurt-bound departures from other European cities for about 40 minutes Friday morning.

Deutsche Bahn AG, Germany's state-owned railway, added additional trains to help cope with the anticipated influx of passengers due to the strike.

Analysts put the financial impact of Friday's strike at between €2 million and €3 million. If the strikes continue, that number could be substantially higher.