The FCA is reopening an investigation into Barclays related to fundraising during the height of the financial crisis.
The reopening of the probe could prompt the FCA, which has been conducting interviews over the last few weeks, to change the amount of the current £50m fine, the Financial Times reports.
The investigation is connected to an emergency cash call, in which the bank sought a £7.3bn boost from Qatari and Abu Dhabi senior royals and sovereign wealth funds in a last ditch effort to escape Government control.
In 2013 the regulator determined that the bank had failed to disclose arrangements and fees it paid to Qatari investors during the fundraising.
The FCA halted its initial probe after the Serious Fraud Office launched an investigation, which included interviews with former chief executives John Varley and Bob Diamond.
That has resulted in the release of 100,000 pieces of documentary evidence by Barclays to the SFO, which is due to conclude its investigation this month.