“This whole experience burst my bubble,” said Mr. Acevedo, a 57-year-old veteran, who lost his case in October 2014. His lawyer, James Cordes, offered a more critical take. “It clearly appears that the arbitrator was working for the company,” Mr. Cordes said. “And he disregarded evidence to hand a good result to his client.”

JAMS denied that its arbitrator had been influenced by CashCall.

Linda S. Klibanow, an employment arbitrator in Pasadena, Calif., acknowledged the potential for conflicts of interest but said she thought most arbitrators, many of whom are retired judges, could remain fair.

“I think that most arbitrators put themselves in the place of a jury as the fact finder and try to render a fair decision,” Ms. Klibanow said.

Elizabeth Bartholet, an arbitrator in Boston who has handled more than 100 cases, agreed that many arbitrators had good intentions, but she said that the system made it challenging to remain unbiased. Ms. Bartholet recalled that after a company complained that she had scheduled an extra hearing for a plaintiff, the arbitration firm she was working with canceled it behind her back.

A year later, she said, she was at an industry conference when she overheard two people talking about how an arbitrator in Boston had almost cost that firm a big client. “It was a conference on ethics, if you can believe it,” said Ms. Bartholet, a law professor at Harvard.

Deborah Pierce, the doctor in Philadelphia, said she did not expect to confront in arbitration the very problem she was suing her employer over: an uneven playing field.

Dr. Pierce decided to go to arbitration after learning that another female doctor had been denied a partnership by her employer, Abington Emergency Physician Associates, under similar circumstances. She also had the backing of the Equal Employment Opportunity Commission, which found that there was probable cause that Dr. Pierce had been discriminated against.