SINGAPORE—Regulators fined ride-hailing firms Grab Inc. and Uber Technologies Inc. and imposed operating restrictions on the former after ruling that a merger earlier this year was anticompetitive.

The Competition and Consumer Commission of Singapore said Monday it would fine Uber 6.6 million Singapore dollars (US$4.8 million) and Grab S$6.4 million. Restrictions on Grab will include a ban on exclusivity agreements with drivers.

The...