An American Airlines pilot terrified passengers when he asked Christians to identify themselves and allegedly went on to call non-Christians "crazy".
Terrified passengers tried to call relatives on their mobile phones
Some passengers on the flight from Los Angeles to New York were so worried they tried to call relatives on their mobile phones.
The pilot, whose name was not released, asked Christians on Friday's flight to raise their hands.
He then suggested non-Christians talk to the Christians about their faith.
He went on to say that "everyone who doesn't have their hand raised is crazy", passenger Amanda Nelligan told CBS news.
"He continued to say, 'Well, you have a choice: you can make this trip worthwhile, or you can sit back, read a book and watch the movie'," she said.
The pilot also told passengers he would be available for discussion at the end of the flight.
A spokesman for American Airlines said later that the pilot denied using the word "crazy".
Ms Nelligan said passengers had thought the pilot's behaviour was "bizarre" and wondered whether his comments were a threat.
Flight attendants notified ground control.
American Airlines spokesman Tim Wagner said the incident was being investigated.
"It falls along the lines of a personal level of sharing that may not be appropriate for one of our employees to do while on the job," he added.