The British bank is also removing a head of global electronic trading for foreign exchange-related misconduct, the New York Department of Financial Services (NYDFS) said. The person's identity was unclear.

The penalty will be reflected in Barclays' fourth quarter 2015 results, the company said. It followed another NYDFS penalty against Barclays in May, bringing total penalties by the regulator against the bank for forex-related conduct to $635 million.

Barclays, in some instances, used a feature called “Last Look” on its forex trading platform to automatically reject client orders that would be unprofitable for Barclays because of price swings in milliseconds-long hold periods the bank imposed after trades were placed.

Barclays, however, did not disclose to clients that the trades were being rejected, but instead cited technical issues or gave vague responses, NYDFS said.

Industry guidelines warn banks not to abuse "last look" rights to reject deals on foreign exchange platforms.

Barclays revised its "Last Look" feature last year, after NYDFS started the forex investigation, to reject trades that were unprofitable to both the bank and customers, the regulator said.

But Barclays did not update one of its trading platforms to work with the revised system, NYDFS said. As a result, 7 percent of Barclays' trading platforms were still filtered by the feature that checked whether trades were not profitable for the bank until August 2015. Barclays has since updated all trading platforms, NYDFS said.

The settlement agreement between NYDFS and Barclays said there were numerous instances in which Barclays staff told employees what to tell clients and the bank's sales staff who questioned why trades were rejected.

Some senior Barclays employees, for example, told traders and technology staff not to let the sales team know about the "Last Look" feature. "If you get inquiries just obfuscate and stonewall,” a Barclays head of automated forex trading wrote in 2011, according to the settlement document, which did not identify the person.

A Barclays sales employee who questioned "Last Look" in 2014 was told by another employee that it was in place to "ensure profitability of a trade for Barclays" but that "Our Team general does not share this info with the client, and just say it was a business reject."

(Reporting by Suzanne Barlyn; Additional reporting by Steve Slater in London; editing by Paul Simao and Meredith Mazzilli, Grant McCool)

By Suzanne Barlyn