The Competition and Markets Authority (CMA) applied them in 1989, after fears two firms, taken over by FirstGroup in 1996, could have too strong a bargaining position with the council.
The CMA said it was seeking views from a number of groups.
First Bristol said it "welcomed the decision to review these undertakings".
The company added it had "already assisted" the CMA as part of the review process.
The restrictions were implemented following the 1989 merger of two local bus companies Badgerline and Midland Red West.
The Monopolies and Mergers Commission, at the time, ruled the merger would remove competition for bus services contracted by the former Avon County Council.
The CMA said the merged company was "therefore required to sign up to a number of restrictions".
These included a cap on the amount they could receive from the local authority for running a tendered service - and a requirement to return any excess profit from such services.
The CMA said it was carrying out the review "to see if there has been a change in circumstances which justifies their removal or variation" and was "seeking views" from local authorities, bus operators and bodies representing bus passengers in Bristol and the surrounding area.
It said it aimed to publish the results of the review in the summer.
Restrictions on bus operator First Bristol, put in place almost 20 years ago, are to be reviewed to "see if they are still appropriate".