The Competition & Markets Authority (CMA) has launched an investigation into the deal between Standard Life and Aberdeen Asset Management.
The watchdog is considering whether the deal would "result in a substantial lessening of competition within any market or markets in the United Kingdom for goods or services".
Standard Life said it had today filed an application with the CMA in respect of the proposed merger with Aberdeen Asset Management.
"This has triggered the CMA’s standard phase 1 review of this application," the savings and investment firm said. "This is one of a number of regulatory approvals being sought as part of the merger process."
Standard Life and Aberdeen announced in March that they had agreed the terms of an £11bn all-share merger.
Earlier this month it emerged that the combination would result in the loss of 800 jobs, around nine per cent of the current combined 9,000 employees.
Meanwhile, both firms will pay out £35m in retention bonuses in order to keep their top executives on board.
Under the terms of the deal, the bosses of Standard Life and Aberdeen, Keith Skeoch and Martin Gilbert respectively, will hold co-chief executive positions.
In March, the firms laid out their plans for how the two men will run the new business, revealing that Skeoch will handle the day-to-day running of the group, while Gilbert will focus on external matters.