Monday was an ugly day on Wall Street, with the Dow Jones Industrial Average and S&P 500 both climbing to substantial early gains before falling sharply late in the session. Major benchmarks posted losses of 1% to 1.6%, with particularly difficult conditions hitting the Nasdaq Composite. New fears of a trade war with China appear closer to becoming reality, and political and macroeconomic uncertainty have many investors afraid that the nearly decade-old bull market is finally coming to a close. Adding to the gloomy mood was news that investors took negatively from several key companies. Amazon.com (NASDAQ:AMZN), Tilray (NASDAQ:TLRY), and Denbury Resources (NYSE:DNR) were among the worst performers on the day. Here's why they did so poorly.

Amazon faces a new tax

Shares of Amazon.com dropped 6% after the U.K. government announced a new tax on large technology companies. Designed to prevent the e-commerce giant and other large companies from earning profits in the U.K. and then escaping taxation overseas, the digital services tax would impose a rate of 2% on sales. With expectations that the tax would generate revenue of 275 million to 400 million British pounds annually, Amazon investors seem to fear that a new trend could pose threats to its efforts to expand internationally, even as it's looking to rising revenue sources like advertising to spur further growth.

Semitrailer with Amazon Prime logo on the side of it

Image source: Amazon.

Cannabis shortages hit Tilray

Shares of Tilray plunged 16% on a bad day for marijuana stocks across the market. Reports from Canada show that shortages of marijuana supplies are hurting sales following the legalization of recreational cannabis products in the country a couple of weeks ago. Key provinces like Ontario and Quebec have been hit especially hard, and some customers have expressed complaints not only about speed of delivery and cancellations of orders but also about the quality of the products delivered. Given how important Canada is as the first-mover among industrialized nations to legalize marijuana, any roadblocks to an efficient rollout of cannabis are bad news for Tilray and its peers.

Denbury makes a deal

Finally, Denbury Resources stock plummeted 24%. The Texas-based energy company announced late Sunday that it would acquire Penn Virginia (Nasdaq: PVAC) in a deal worth $1.7 billion. Under the terms of the acquisition, Penn Virginia investors will get $25.86 in cash plus 12.4 shares of Denbury for every share of Penn Virginia they own. Denbury CEO Chris Kendall called the transaction "a defining moment," pointing to Penn Virginia's assets in the valuable Eagle Ford play as helping its overall strategic vision. Yet investors worry that Denbury's attempt to diversify its exposure could backfire if it can't get up to speed quickly -- especially with crude oil prices falling another $1 per barrel today.

John Mackey, CEO of Whole Foods Market, an Amazon subsidiary, is a member of The Motley Fool's board of directors. Dan Caplinger has no position in any of the stocks mentioned. The Motley Fool owns shares of and recommends Amazon. The Motley Fool has a disclosure policy.