US authorities have hit Lufthansa with a record $4 million penalty after finding the airline discriminated against more than 100 Jewish travelers by blocking them from boarding a flight in 2022, officials said Tuesday.

The 128 passengers were denied boarding to a connecting flight after a few did not follow instructions, including Covid mask requirements, on a flight from the United States to Germany, US transport authorities said.

The US Department of Transportation said the penalty over the boarding refusal on May 3, 2022 in Frankfurt was the largest it had issued for a civil rights violation.

The travelers — who wore distinctive garments including black hats and jackets — told investigators they were treated as if they were one group, even though many were not flying together and did not know each other.

Lufthansa denied boarding “to everyone for the apparent misbehavior of a few, because they were openly and visibly Jewish,” DOT authorities said in a filing.

The problem began when the captain of the first flight reported to Lufthansa security that some passengers were not following rules, including wearing face masks during the trip and not standing in groups in aisles or near emergency exits.

DOT authorities received more than 40 discrimination complaints from Jewish passengers in this case.

Lufthansa told DOT that it has publicly apologized on numerous occasions for barring the passengers from continuing their trips, but denied any suggestion that any of its employees engaged in any form of discrimination.

In a statement following the announcement of the fine, the airline said it had implemented a new training program “to address anti-Semitism and discrimination.”