FRANKFURT (Reuters) - Lufthansa's cabin crew union has called on its members to strike at Lufthansa and short-haul carrier CityLine on Tuesday and Wednesday to press their demands for higher pay.

The UFO union of flight attendants said on Saturday that the strike, which was voted for by members, would affect departures from Frankfurt airport on Tuesday and departures from Munich on Wednesday.

Lufthansa said about 100,000 passengers would likely be affected.

The airline group warned on Thursday its operating losses in the first quarter will widen and gave a subdued outlook for 2024 as it struggles with costly labour disputes, offsetting a travel boom.

Europe's airlines have benefited from unprecedented demand since the pandemic, allowing them to raise prices, but higher labour and maintenance costs have limited earnings growth.

Lufthansa in particular has agreed to new, higher pay deals to end strikes, which analysts and investors say threaten its 2024 operating margin target.

On Thursday, Lufthansa ground staff walked off the job, while on Wednesday cabin crew voted to strike as they seek a 15% wage increase.