A pilot has refused passage to a group of Russian wheelchair users heading to a seminar in Germany about improving accessibility in urban spaces.

The 34-strong delegation was set to depart from Moscow’s Domodedovo Airport on an AirBerlin flight to Dusseldorf, said State Duma deputy and delegation member Vladimir Krupennikov.

But the pilot refused to fly with more than two wheelchair users on board, citing the carrier’s internal safety regulations, said Krupennikov, himself a wheelchair user.

In the end, 11 group members, including six wheelchair users, failed to board the plane and had to find another flight to Dusseldorf, he said.

Those stranded are planning to sue AirBerlin for damages, Krupennikov said.

The company had one month’s warning that a large group of people with special needs will be flying on Monday, and gave written authorization, he explained.

As of Monday afternoon, the carrier had not commented on the incident. Its press service could not be reached by telephone or email.

AirBerlin generally takes a positive attitude toward people with special needs, and Monday’s incident may have been a “misunderstanding,” said Alexander Lomakin-Rumyantsev, who heads the All-Russia Society for the Disabled.

But similar incidents have happened in Russia. In April, Vladivostok Air refused a woman with only one leg passage from Moscow to Ulan-Ude. The carrier S7 lost two lawsuits in 2008 and 2009 over refusing to let disabled people on board.