Fresh off its biggest Prime Day yet, the Whole Foods Market Inc. bid, and a slew of announcements including Amazon Wardrobe, Amazon.com Inc. was the subject of two investor calls last week that raised concerns that it is getting too big.

In one case, hedge-fund manager Douglas Kass said government intervention could be imminent.

“I am shorting Amazon today because I have learned that there are currently early discussions and due diligence being considered in the legislative chambers in Washington DC with regard to possible antitrust opposition to Amazon’s business practices, pricing strategy and expansion announcements already made (as well as being aimed at expansion strategies being considered in the future,” wrote Kass, head of Seabreeze Partners Management.

See: It’s time to bet against Amazon, says money manager Doug Kass

Kass said he is taking a short position on the stock, or a bet that it will fall. The investor said the stock could fall 10% overnight once the market gets wind of the talks.

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Amazon is buying Whole Foods: What you need to know

As Amazon AMZN, -1.78% has grown, so has speculation about which retail category it will rule next. The company already dominates books, the cloud and electronics. And with moves in fashion and grocery, it appears the company has its eye on those sectors next. Its dominance has created major stress for brick-and-mortar retailers, who are suffering badly as they scramble to catch up.

In January, European Union antitrust regulators cheered the end of audiobook exclusivity between Amazon and Apple Inc. AAPL, -3.17% And last August, Amazon’s offices in Tokyo were searched by the Fair Trade Commission on suspicion that it was breaking antitrust laws.

Amazon said Wednesday that Prime Day was its biggest day ever, with sales up 60% from the same 30-hour period the previous year. The Echo Dot was the best seller, and the company said it gained more new Prime members on July 11 than any other day in its history. As usual, it did not provide any hard numbers.

Kass bolstered his argument in a Thursday comment.

“My understanding is that certain Democrats in the Senate have instituted the very recent and preliminary investigation of Amazon’s possible adverse impact on competition,” he said. “But, in the Trump administration we also have a foe against Jeff Bezos, who not only runs Amazon but happens to own an editorially unfriendly (to President Trump) newspaper, The Washington Post.”

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Amazon has been busy this summer, announcing its purchase of Whole Foods US:WFM last month. Within days, it announced Amazon Wardrobe, a service that lets shoppers try on clothing and receive discounts when they purchase multiple items. Shortly after that, Nike Inc. NKE, -1.46% confirmed that it would begin selling a limited assortment on Amazon.

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Read: Amazon ‘will be a top 5 grocer in the U.S.’ with Whole Foods acquisition

Kass said he thinks the government “discussions may have just begun and may never result in any serious effort to limit Amazon’s growth plans.” But he has been writing a series of columns about whether we’ve reached “peak Amazon,” and said in an earlier column that the Whole Foods deal puts “Amazon’s vast power… under the microscope.”

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“Is Amazon a productive change agent and force for the good of the consumer by virtue of a reduction in product prices? Or is Amazon’s disruption of the general retail business a destroyer of jobs, moving previously productively employed workers into the unemployment line?” he asked.

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Kass has previously expressed doubts about Amazon, saying in October 2014 that investors should “avoid Amazon at all costs” and that the company “continues to fail to exhibit a cash flow return on any investment it makes.” The stock has more than tripled in value since then.

Steve Kaplan, a trader and True Contrarian blogger, joined Kass on Wednesday with a short position of his own. Kaplan said Janet Yellen is incorrect and that a recession is looming. He is skeptical about a few other big names too.

“We are likely to experience an especially severe recession since so much money has come out of safe time deposits like bank accounts and money-market funds and has gone into fluctuating assets including real estate, corporate bonds, stocks, and especially the most popular overpriced garbage including Amazon, Tesla TSLA, +4.42% , Netflix NFLX, -0.05% , Nvidia NVDA, -2.20% , etc.,” Kaplan said.

Amazon shares are up 0.7% Monday, and have gained 35% in the year so far. The S&P 500 index SPX, -1.11% is up 10% for 2017 to date.

Additional reporting by Barbara Kollmeyer