TikTok's head honcho Shou Zi Chew posted a video Wednesday in response to Joe putting his John Hancock on legislation that got passed in the House of Representatives and the Senate ... which basically makes TikTok illegal here in the States under Chinese control.

The businessman says he and his partners are going to challenge this new law -- and is confident TikTok will win before a judge, stating the Constitution is on the company's side. Chew and co. say they're going to cite First Amendment rights in defending their position.

Chew then blasted the politicians ... saying a TikTok ban has always been their goal, and says them trying to force this down Americans' throats is counter to what the people want.

He adds ... "It's obviously a disappointing moment, but it does not need to be a defining one. This is actually ironic, because the freedom of expression on TikTok reflects the same American values that make the United States a beacon of freedom."

ICYMI ... Congress voted in favor of legislation which would see TikTok banned if ByteDance, a Chinese tech firm, doesn't divest from the short-form social media platform in the next several months.

Lawmakers have cited privacy concerns over TikTok, including possible spying ... not to mention the notion Chinese propaganda might be getting pushed onto users here in America.

Of course, a lot of U.S.-based TikTokers have cried foul ... expressing their love for the app.

Now, it's officially happening ... and everyone's got about 9 months before this thing is gone for good -- that is, unless TikTok is successful in reversing this decision in their legal challenge.