Donald Trump threatened a 100% tariff on European countries that impose a digital services tax, as the president once again came to the defense of American tech giants that have opposed the levies.

It wasn’t immediately clear under what authority Trump would impose the tariff, given the Supreme Court decision earlier this year that struck down his sweeping global tariffs, the foundation of his economic agenda.

Trump posted on Truth Social on Friday, “Numerous European Countries have been discussing the imminent implementation of a Digital Services Tax on American Companies. Some of these Countries are close to actually doing this. Please let this statement serve to represent that any Country that imposes such a Tax will immediately be met with a 100% TARIFF on any and all Goods sent to the United States of America. This TARIFF will supersede Trade Deals made with the Country, whether implemented, signed, or not. Additionally, the 100% TARIFF will be immediately imposed, if they proceed. Thank you for your attention to this matter. President DONALD J. TRUMP”

According to the Tax Foundation, about half of all European Organization for Economic Cooperation and Development countries “have either announced, proposed, or implemented a DST.”

Trump had set a July 4 deadline for the European Union and the United States to put into effect a trade deal that caps European imports at a 15% tariff, but digital taxes were not part of the agreement, per the AP.

Last year, Trump threatened to cut off trade talks and a new tariff with Canada as it looked to implement a digital services tax. That 3% tax was repealed earlier this year.