British Airways says it is checking in passengers “as normal” on Tuesday, following massive problems with its check-in systems that seem to have affected customers in North America and Europe since Monday.

The carrier, owned by International Consolidated Airlines Group icagy , had to field complaints from people stuck in long queues at airports from Toronto to San Francisco to London.

On top of that, protesters from the Black Lives Matter U.K. movement gained access to the runway at London City Airport and locked themselves together there, blocking all flights at the airport.

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Many BA passengers took to Twitter to complain about the technical difficulties that were affecting their check-in.

Some shared pictures of the handwritten boarding passes they had been given.

“We are checking in customers this morning as normal, although it may take longer than usual,” BA said in a Tuesday statement. “We would encourage customers to check in online before they reach the airport.”

London City Airport is the capital’s smallest airport, mainly serving business passengers—it’s close to the Canary Wharf financial district.

The Black Lives Matter activists said they were protesting there because it serves a “small elite” while thousands of non-European migrants are dying while trying to cross the Mediterranean.

They also said they were protesting against climate change.