Microsoft Corp. and an Amazon Inc. unit’s dominance in the cloud services market must face an antitrust investigation under the UK’s new rules for digital markets, the country’s watchdog said after 21 month-long investigation.

Britain’s competition regulator called for a probe into Microsoft and Amazon’s cloud market dominance under the country’s strict new tech rules.

Britain’s competition regulator is set to deepen its probe into the UK cloud services market, targeting Microsoft and Amazon over their combined dominance in the infrastructure-as-a-service (IaaS) sector.