What happened It's Wednesday, and the stock market is in full retreat (yep, again), with the S&P 500 tumbling 2.2% as of 1 p.m. EDT. Shares of travel-industry-related stocks are taking it especially hard, with shares of reservations specialist Booking Holdings (NASDAQ: BKNG) down 4.2%, hotelier Marriott International (NASDAQ: MAR) off 5%, and rental-car company Avis Budget Group (NASDAQ: CAR) crashing 7.8% lower. I see two big reasons for that -- both are "macro," but only one has the word "coronavirus" in it. Image source: Getty Images. So what Microeconomically speaking, today is kind of a slow news day for Booking, Marriott, and Avis. Since Marriott received the pleasant surprise of a price-target hike yesterday (from Nomura Instinet, which thinks the $86 stock is worth nearly twice that), there's been nary a peep out of Wall Street that might have spooked investors. Macroeconomically, however, the market's worried that the Trump Administration is about to start a trade war with Europe. In response to European Commission moves to tax digital transactions and target the profits of U.S. tech companies like Facebook, Google, and Amazon, President Trump's trade negotiators are threatening to raise tariffs on some $3.1 billion in goods imported from France, Germany, Spain, and the U.K. (Trump's also apparently eyeing Canada for a new tariff on aluminum imports, so there's really trade-war risk all around.) And that's not the worst of it. Trade wars involving imported goods probably wouldn't affect stocks providing travel services directly. But at the same time as that threat is brewing, we're hearing new reports from the National Institute for Allergies and Infectious Diseases (Dr. Fauci's outfit) that the majority of U.S. states are now reporting rising incidences of coronavirus infection -- the exact opposite of what you'd want to see if we have truly succeeded in "flattening the curve." Texas, in particular, just set a new record (for that state) of 5,000 new coronavirus cases reported in a single day, and across the nation, the U.S. now has 2.35 million reported cases -- more than twice the next worst-hit country in the world (which would be Brazil). Now what In short, COVID-19 has once again reared its ugly head and sparked fear in the market. Fearful people don't make plans to travel (Booking Holdings). They don't reserve hotel rooms at vacation destinations (Marriott). And for that reason, they don't reserve rental cars to cart themselves around once they reach those destinations (Avis Budget). This, in a nutshell, is why you're seeing shares of Booking Holdings, Marriott International, and Avis Budget Group stocks going down today. 10 stocks we like better than Marriott InternationalWhen investing geniuses David and Tom Gardner have a stock tip, it can pay to listen. After all, the newsletter they have run for over a decade, Motley Fool Stock Advisor, has tripled the market.* David and Tom just revealed what they believe are the ten best stocks for investors to buy right now... and Marriott International wasn't one of them! That's right -- they think these 10 stocks are even better buys. See the 10 stocks *Stock Advisor returns as of June 2, 2020 John Mackey, CEO of Whole Foods Market, an Amazon subsidiary, is a member of The Motley Fool's board of directors. Suzanne Frey, an executive at Alphabet, is a member of The Motley Fool's board of directors. Randi Zuckerberg, a former director of market development and spokeswoman for Facebook and sister to its CEO, Mark Zuckerberg, is a member of The Motley Fool's board of directors. Rich Smith has no position in any of the stocks mentioned. The Motley Fool owns shares of and recommends Alphabet (A shares), Amazon, Booking Holdings, and Facebook. The Motley Fool recommends Marriott International and recommends the following options: short January 2022 $1940 calls on Amazon and long January 2022 $1920 calls on Amazon. The Motley Fool has a disclosure policy.Source