The U.S. antitrust enforcers have been asking software companies about practices around Amazon's cloud unit Amazon Web Services, the report said.

Big tech companies such as Facebook Inc, Alphabet Inc Google, Apple Inc and Amazon face a slew of antitrust probes by the federal government, state attorneys general and congress.

FTC's Technology Enforcement Division was focussing its probes of multi-sided platforms on illegal conduct and mergers that previously won antitrust approval.

FTC and Amazon declined to comment on the report.

In cloud computing, one of the fastest-growing areas in the technology industry, businesses rent out servers from Amazon instead of running their own data centres.

Amazon is the biggest cloud services provider, competing most closely with Microsoft Corp. Smaller companies also compete to provide services on cloud networks to developers and corporate customers.

Analysts expect Amazon's cloud unit to generate $34.9 billion in sales in 2019, according to IBES data from Refinitiv.

In addition to the FTC probes, the Justice Department and House of Representatives Judiciary Committee are investigating all four big tech companies.

(Reporting by Rishika Chatterjee, additional reporting by Neha Malara in Bengaluru, Editing by Sherry Jacob-Phillips)