Two brokers at a Beverly Hills office of Bank of America's Merrill Lynch must collectively return more than $6.6 million in signing bonuses to Barclays Capital for leaving the firm's U.S. broker unit after working only three-and-a-half months, a regulatory panel has ruled.

Matthew Celenza was ordered by a Financial Industry Regulatory Authority (FINRA) arbitration panel on Friday to pay $5.1 million representing principal on a note he signed when joining Barclays in March 2012, plus almost $140,000 in interest.

Lawrence DiGioia, Celenza's partner, was ordered to pay $1.51 million on the principal part of his note and just over $41,426 in interest. The FINRA panel also raised the annual interest rate on any amount not repaid as of the end of last month from 1 percent to 5 percent until it is paid in full.

A person answering the phone Monday at the six-person Celenza & DiGioia Group said the two were not available for comment.

Big brokerage firms in the United States typically offer signing bonuses to top brokers in the form of loans that are forgiven over a period of time that typically runs about eight years. Barclays cited unjust enrichment, breach of contract, and performance, among other causes, in its claim.

The arbitrators did not explain their decision, as is typical in FINRA rulings, but denied the brokers' counterclaims asserting fraud, negligent misrepresentation, and breach of contract to justify keeping the loans.

"Barclays is pleased with the outcome of this case and that all of their claims were dismissed in their entirety," said a spokeswoman at the bank.

The arbitration panel denied Barclays' effort to require the brokers to pay its attorneys' fees.

"Barclays asked for more than $1 million and got zero, so the panel obviously thought something was amiss," said Jeff Riffer, a lawyer at Elkins, Kalt, Weintraub, Reuben Gartside who represented Celenza and DiGioia.

The brokers argued that Barclays broke a promise to develop a life insurance product for them to sell to clients, their lawyer said. He also cited an "intolerable" cultural climate that ultimately led to the dismissal of Barclays' top wealth executives in London and the U.S. to explain his clients' brief sojourn at theBarclays Plc unit.

Celenza and DiGioia have not decided whether to take the rare move of seeking to vacate the FINRA arbitration decision, Riffer said.

A Merrill Lynch spokesman declined to comment on whether the firm would pay any of the brokers' costs.

Jeff Goldberg, a lawyer at Palmer, Lombardi & Donohue, which represented Barclays, said he was not authorized to speak immediately on behalf of his client.

Celenza and DiGioia joined Barclays for their short stint in March 2012 after working 12 and 11 years, respectively, at Morgan Stanley and predecessor firm Smith Barney, according to FINRA's BrokerCheck database.