The FSA has fined Credit Suisse £2.5m - reduced to £1.75m due to early settlement - for failing to submit accurate transaction reports.
The investment bank failed to submit accurate data on about 40 million separate transactions - including 30 million on the London Stock Exchange (LSE) - in a 12 month period from November 2007.
Market trader Getco and agency broker Instinet were also fined a total of £2.45m, taking the total FSA penalty to £4.2m.
The City regulator says it uses transaction data to detect and investigate suspected market abuse, insider trading and market manipulation.
"Without quality data we cannot properly detect and investigate market abuse, identify market wide risks or have a comprehensive understanding of the activities of each firm," the FSA's director of markets Alexander Justham says.
"The standard of regulatory reporting by these firms fell far short of what the FSA expects and requires."
Between 5 November 2007 and 20 November 2008, Credit Suisse failed to submit accurate data on about 40 million transactions, including on every single LSE deal it was involved in.
The FSA says the firms could have prevented the breaches with regular data reviews, and sent all three firms repeated warnings in 2007 and 2008.
It adds the failures were exacerbated because they occurred during a period of heightened awareness around transaction reporting issues as a result of the implementation of the Markets in Financial Instruments Directive (MiFID).
