WASHINGTON (Reuters) - Amazon.com Inc AMZN.O shares fell almost 5 percent on Wednesday, wiping more than $30 billion off its market value, after news website Axios reported that U.S. President Donald Trump is obsessed with the world's largest online retailer and wants to rein in its growing power.

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Trump has talked about using antitrust law to “go after” the company because he is worried about mom-and-pop retailers being put out of business by Amazon, Axios reported, citing five sources it said had discussed the issue with him.

Trump also wants to change Amazon’s tax treatment, the Axios report said, an issue the president raised publicly last year when he called for an internet tax for online retailers, even though Amazon already collects sales tax on items it sells direct to customers.

“The president has said many times before he’s always looking to create a level playing field for all businesses and this is no different,” said White House spokeswoman Sarah Sanders, when asked about the Axios report. “He’s always going to look at different ways, but there aren’t any specific policies on the table at this time.”

Trump has been complaining about Amazon in private, believing the company has become too powerful, another administration official confirmed to Reuters.

The official said Trump links this to Amazon Chief Executive Jeff Bezos’ private ownership of the Washington Post, which he has called “fake news” for its critical coverage of his administration. Trump regards the newspaper as a mouthpiece for Bezos’ business interests, calling it #AmazonWashingtonPost on Twitter.

Amazon did not reply to a request for comment on the Axios report.

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Trump has criticized Amazon over taxes and jobs in the past, without offering evidence. The president urging the use of antitrust law to selectively thwart a company would be unprecedented, according to Jeffrey Jacobovitz of the law firm Arnall Golden Gregory LLP.

Amazon’s stock, which fell as low as $1,386.17 on Wednesday, was last down 4.6 percent at $1,427.83. The shares have nearly quadrupled over the last three years.

Tech stocks have been under pressure after Facebook Inc FB.O acknowledged this month that user data had been improperly harvested by a consultancy.

“With Facebook and regulatory worries, the last thing nervous tech investors wanted to see was news that Trump is targeting Bezos and Amazon over the coming months as this remains a lingering cloud over the stock and heightens the risk profile in the eyes of the Street,” GBH Insights analyst Daniel Ives said.