The political network backed by billionaire Charles Koch launched an ad blitz targeting Sens. Joe Manchin and Kyrsten Sinema to get the moderate Democrats to block a massive spending-and-tax package that’s advancing in the Senate.

The bill, known as the Inflation Reduction Act of 2022, promises to raise $739 billion in new revenue — mostly by setting a minimum corporate tax rate and making changes to Medicare drug pricing — to help pay for $433 billion in climate and health initiatives.

The legislation is a pared-down version of President Joe Biden’s Build Back Better plan, which failed earlier this year after Manchin and Sinema opposed key elements of the bill. The legislation has a renewed chance of passing after Manchin reached a deal last week on a smaller tax-and-spending package with Senate Majority Leader Chuck Schumer, D-N.Y. It represents one of the most important pieces of legislation for Democrats as they fight to hold on to the Senate with the November midterms just under 100 days away. Manchin and Sinema, who are both up for reelection in 2024, represent key votes in the Senate, with the chamber split 50-50.

Americans for Prosperity, which is part of the larger Koch network, launched two ads on Saturday on its Facebook, Twitter and YouTube pages. The ads specifically call out the two senators, encouraging them to oppose the legislation. “Senator Manchin can stop it. Come on, Joe … Say NO for West Virginia,” the Manchin-focused ad says. The Sinema ad has an almost identical look, stating “Senator Sinema can stop it. Come on, Kyrsten … Say NO for Arizona.”