Small-business merchants listing their wares on  (AMZN) - Get Report are being questioned by Federal Trade Commission officials to determine if the e-commerce giant is exerting undue influence and stifling competition.

Bloomberg reported that a team of FTC investigators including several attorneys and at least one economist has begun interviewing Amazon small-business sellers on a range of topics, three merchants told the news service.

All were asked what percentage of revenue their businesses derive from Amazon vs. other online marketplaces like Walmart (WMT) - Get Report and eBay (EBAY) - Get Report  - an indication that regulators are zeroing in on how much choice both sellers and consumers have in choosing Amazon over others, according to Bloomberg.

The length of the interviews as well as the resources devoted by the FTC to examining Amazon suggest a more serious inquiry, Bloomberg said.

Amazon declined to comment, pointing Bloomberg to a statement Consumer Business Chief Jeff Wilke made in June when asked about reports that the FTC was looking into Amazon.

"We believe that most substantial entities in the economy deserve scrutiny," he said. "Our job is to build the kind of company that passes that scrutiny with flying colors."

The probe is part of a broader examination of the control companies like Amazon, Alphabet's Google (GOOGL) - Get Report and Facebook (FB) - Get Report have over the U.S. economy. The FTC also is investigating Facebook, while the Justice Department is probing Google.

Separately, 50 state attorneys general announced last month an antitrust probe of Google. The House Judiciary Committee is also probing big technology companies.

Amazon shares were little changed at $1,813.82 in early New York trading on Wednesday.

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