Judge Alison Russell ruled against of the bank in its dispute with Perry Stimpson, a forex trader in London who was fired in November 2014.

The decision is seen as a significant test case as it is the first of several cases due to be heard at London employment tribunals by former traders dismissed in the wake of investigations into alleged manipulation of foreign exchange and benchmark Libor rates.

Stimpson said he was unfairly dismissed by Citigroup, which fired him for sharing confidential client information with other traders. Stimpson had said the sharing of information in chatrooms was known and condoned by senior management.

The hearing was heard at the East London Employment Tribunal between September 8 and 17.

(Reporting By Steve Slater, editing by Anjuli Davies)