The move: US media stocks tumbled lower on Monday. Here are some of the biggest moves:

Why: Investors sold shares of some of the top streamers and movie companies as President Donald Trump said he would instruct the Commerce Department to institute a 100% tariff on foreign-made movies.

In a post on Truth Social, Trump suggested that tax incentives offered by other nations were drawing filmmakers away from the US, which he referred to as a “National Security threat.”

“The Movie Industry in America is DYING a very fast death,” Trump wrote. “WE WANT MOVIES MADE IN AMERICA, AGAIN!” he later added.

What it means: US production companies film overseas for various reasons, including tax incentives offered by other countries to attract filmmakers. The tariff could represent a steep cost for an industry that had otherwise been out of the crosshairs of the trade war.

The potential film tariff is also another indication that Trump is escalating his trade war, despite the White House reporting progress on trade negotiations with other countries.

The development is coming after a strong quarter for top film stocks. Netflix and Disney both posted earnings and revenue beats over the first quarter, sending the share prices of each stock higher.