HSBC, based in London, and Citigroup, with headquarters in New York, each suspended two currencies traders against the backdrop of the investigation that began in April, the Journal said.
The HSBC suspensions were the first the financial institution has carried out since the probe began.
Before suspending currencies traders in London and New York Thursday, Citigroup fired its chief trader for major currencies in Europe last week.
Citing someone is described as familiar with the situation at Citicorp, the Journal reported the traders were suspended after the bank discovered "inappropriate electronic communications."
Several other banks also suspended currencies employees.
A global investigation into practices by currencies traders began when Britain's Financial Conduct Authority started looking into foreign currency trading after a complaint by an asset manager. Soon after, regulators in the United States, Switzerland and other countries joined the investigation.
The Journal said some regulators asked banks to sift through messages between traders for indications of possible collusion or other unfair methods of making profits around currencies benchmarks.