As soon as Amazon announced on Friday that it was purchasing Whole Foods for $13.7 billion, antitrust and competition policy experts sat straight up.

While Amazon has been toying with brick-and-mortar retail for a few years — opening a handful of bookstores and grocery stores — the Seattle digital retail giant’s domination has mostly stayed online. Amazon accounted for 34 percent of all digital commerce last year, and that figure is expected to hit 50 percent by 2021, according to figures from the research firm Needham & Co.

The reaction on Wall Street to the Amazon-Whole Foods announcement suggests that investors expect Amazon to extend that dominance to supermarkets; since the deal was revealed, Amazon’s market value has risen by more than the $13.7 billion it’s paying for Whole Foods.

Rival supermarket, big-box, and online retailers, meanwhile, have seen billions of dollars collectively lopped off their share prices, in spite of the fact that Whole Foods only controls about 1.2 percent of the U.S. grocery market. Walmart, Target, and Kroger (about 24 percent of the market, taken together) are all trading at least significantly below their market open today.

This kind of power play from Amazon is raising eyebrows among a number of antitrust experts and at least one Democratic congressman. The concern is that Amazon will gain even more leverage to negotiate costs with its suppliers in order to lower prices as much as possible, in turn giving it an insurmountable competitive edge over rivals online and IRL.

“If approved by regulators, the deal would worsen the already severe damage that Amazon is doing to America’s competitive, open market system,” said Barry Lynn, director of the Open Markets program at the New America Foundation.

Ro Khanna, a Democratic congressman whose district encompasses a significant chunk of Silicon Valley, said in a statement to VICE News that he is “concerned about what this deal means for suppliers and neighborhood grocery stores.”

“The Justice Department and Federal Trade Commission must undertake a review that considers not just the merger’s impact on prices but also the impact on jobs and wages. We need to reorient antitrust policy to factor in the harm that economic concentration causes for American workers,” Khanna said. “We also need to be mindful that concentrated industries stifle innovation. American markets work best when there is fair competition among many businesses — none of which have a dominant market share.”

Whether the skepticism and calls for FTC and DOJ reviews will actually amount to anything remains to be seen. Both the Justice Department and the FTC declined to comment, but one former lawyer in the FTC’s Bureau of Competition told VICE News that “this has potential to become a big fight on the antirust front.”

Two big factors are whether the Democrats choose to take up this battle, and whether Donald Trump follows up on campaign promises to block big mergers. Even though Trump has directly called out Amazon CEO Jeff Bezos for Amazon’s “huge antitrust problem,” the Trump administration has mostly taken a passive role with mergers that the president had criticized on the campaign trail.