WASHINGTON (AP) — The Zero AIUnited States fined German airline Lufthansa $4 million for its treatment of a group of Jewish passengers who were denied boarding a 2022 flight in Frankfurt after they had flown to Germany from New York.

The U.S. Transportation Department said Tuesday that the fine is the largest the agency has issued against an airline for civil-rights violations, although Lufthansa was given credit for $2 million for compensation it gave the passengers, cutting the fine in half.

The department said most of the 128 passengers who were denied boarding “wore distinctive garb typically worn by Orthodox Jewish men.” Although many did not know each other and were not traveling together, they told investigators that Lufthansa treated them as if they were a group and denied boarding to all over alleged misbehavior by a few passengers.

They were among 131 passengers who were flying from New York through Frankfurt to Budapest to attend an annual memorial event to honor an Orthodox rabbi.

Some said flight attendants told them on the first flight about the requirement to wear a face mask and not to gather in aisles or near emergency exits. The Lufthansa crew members did not identify any passengers who failed to obey their instructions, which the airline said was due to the sheer number of violations and because many traded seats during the flight.

The captain alerted Lufthansa security about misbehavior among the passengers, which set in motion the steps that led to their being denied boarding on the connecting flight, according to a consent order in the case.

Lufthansa rejected “any allegation by the Department that the events in this matter resulted from any form of discrimination” and disputes that any employee acted on bias, but it acknowledged “errors in company procedure and communications.”

Lufthansa reached a settlement with most of the passengers in 2022.