The Competition and Markets Authority (CMA) has launched an inquiry into the £11bn tie-up planned by Standard Life and Aberdeen.
In an announcement, the CMA said it was considering whether the merger "may be expected to result in a substantial lessening of competition" within the UK.
The competition watchdog has invited comment by June 6, and will then decide in July whether to take the process any further.
The two asset managers, who announced merger plans in March, intend to combine to form a fund house with £660bn in assets under management. The deal is expected to close in August.
Standard Life said in a statement: "Standard Life today filed an application with the CMA in respect of the proposed merger with Aberdeen Asset Management.
"This has triggered today's announcement by the CMA that the standard phase 1 review of this application is now underway. This is one of a number of regulatory and antitrust approvals being sought as part of the merger process."
