Sen. Marco Rubio is on the verge of tanking the defense spending bill over an amendment on forced Uyghur labor from China

• Republican Sen. Marco Rubio of Florida made an unexpected move Wednesday night.
• Rubio proposed an amendment that could tank the National Defense Authorization Act.

Bringing the $740 billion National Defense Authorization Act to a screeching halt Wednesday night, GOP Sen. Marco Rubio of Florida is standing by an amendment that Senate Majority Leader Chuck Schumer described as a "poison pill."

The reason Rubio's amendment threw a wrench into the gargantuan bill comes down to complicated but nonetheless longstanding Congressional procedures.

Rubio wants an amendment in the bill that would ban US imports from China's Xinjiang region, citing forced labor imposed upon the Uyghur population. Around 1 million Uyghurs — a mostly Muslim ethnic minority native to the region — are estimated to be in Chinese internment camps.

The Florida senator's amendment was not included in a package of amendments the Senate voted on Thursday night because of what's known as a "blue slip" problem, meaning Rubio's amendment involves revenue for the US government and thus requires a House vote.

"The Rubio amendment is a poison pill [in the] sense it blows up the whole bill," Schumer said, according to Politico's Andrew Desiderio.

The crux of the issue goes back to the Constitution.

In section 7 of Article 1 — more commonly referred to as "the power of the purse" — the founders determined that any bill that raises revenue must originate in the House.

Since the Rubio amendment would entail tariff revenue from imports, it would need to be kicked over to the other chamber.

Late Wednesday night, a Rubio spokesperson blasted Schumer for "creating fake procedural excuses to avoid a vote on slave labor," according to Politico.

In an email to Insider, a Rubio spokesperson further disputed Schumer's "poison pill" assessment.

"Shortly before Thanksgiving, Senate Democrats would not let Senator Rubio get a vote on his Uyghur Forced Labor Prevention Act as part of the annual defense bill process," the Rubio representative told Insider. "As a result, Marco objected to the amendment agreement. As a reminder, this bill passed the Senate unanimously this summer but the House has not taken action."