Britain's financial watchdog fined Barclays 2.45 million pounds ($4 million) on Tuesday for failing to provide accurate transaction reports and "serious weaknesses" in control systems in two of its divisons.
The Financial Services Authority levied the penalty on Barclays Capital Securities and Barclays Bank.
Financial institutions are required to submit transactions data by close of business the day after a trade is executed. The FSA uses this to detect and investigate suspected market abuse like insider trading and market manipulation.
The FSA said it discovered discrepancies in Barclays' data while reviewing a suspected incident of market abuse by a third party.