• The Koch network has been actively pressuring Democratic Sen. Joe Manchin to oppose key legislative items linked to Biden's agenda, including filibuster reform and voting rights legislation.
• The lobbying effort appears to be paying off. Manchin, in a recent op-ed, wrote that he opposed eliminating the filibuster and that he would not vote for the For the People Act.
• The Koch network specifically calls on its grassroots supporters to push Manchin, a conservative Democrat, to be against some of his party's legislative priorities.

The political advocacy group backed by billionaire Charles Koch has been pressuring Sen. Joe Manchin, D-W.Va., to oppose key parts of the Democratic agenda, including filibuster reform and voting rights legislation.

That lobbying effort appears to be paying off. Manchin, in a recent op-ed, wrote that he opposed eliminating the filibuster and that he would not vote for the For the People Act, which, advocates say, would limit the influence of big donors on elections.

President Joe Biden has called some of the voting restrictions proposed by Republican leaders in several states "sick" and "un-American." The president has praised the For the People Act and has said the filibuster must be changed.

Sixty votes are needed to break the filibuster in the Senate in order to allow legislation to get a final vote. Democrats, who have 50 seats, have narrow control of the chamber because of Vice President Kamala Harris' tie-breaking vote.

CNBC reviewed an episode of a Koch policy group Americans for Prosperity's video series, along with ads crafted by the organization. The network specifically calls on its grassroots supporters to push Manchin, a conservative Democrat, to be against some of his party's legislative priorities.

Americans for Prosperity launched a website titled West Virginia Values, which calls on people to email Manchin "to be The Voice West Virginia Needs In D.C. — Reject Washington’s Partisan Agenda."

It then lists all of the items Manchin has promised to oppose, including the idea of eliminating the filibuster, the For the People Act and packing the Supreme Court. It then shows everything the group believes Manchin should oppose, including Biden's infrastructure plan and the union-friendly PRO Act.

Americans for Prosperity leaders took part in one of their video series with their West Virginia state director in May where they praised Manchin for voicing his opposition to abolishing the filibuster. Both Americans for Prosperity and Manchin have said they believe eliminating the filibuster would exacerbate partisanship.

The video was reviewed by CNBC after it was posted to the group's Facebook page.

"A wise man once said that it takes a lot of courage to stand up to your enemies but that it takes even more courage up to stand up to your friends," Ted Ellis, director of coalitions for Americans for Prosperity's government affairs team, told the audience. "And that's what Joe Manchin is doing right now. He's displaying, I think, a lot of courage and we should applaud that."

"Our grassroots are critically important and it would be difficult to say that they are more important anywhere than West Virginia right now because of the dramatic impact that our grassroots have in West Virginia in encouraging Senator Manchin to stand strong on this point," Casey Mattox, vice president of legal and judicial Strategy at Americans for Prosperity, said during the presentation.

Ellis is listed on a recent lobbying report as one of the Americans for Prosperity officials who in the first quarter of 2021 lobbied against the For the People Act and Biden's $1.9 trillion coronavirus relief plan. The lobbyists targeted House and Senate lawmakers.

In a statement to CNBC, a spokesman for Americans for Prosperity did not deny whether its officials have spoken directly to Manchin or his staff about the For the People Act. The representative praised Manchin's stance on the bill and likened the group's stance to that of the American Civil Liberties Union.

"Sen. Manchin has long blazed his own path, and on this issue, we agree: Extreme partisanship gets in the way of finding positive solutions," Lo Isidro, a spokesman for AFP, told CNBC in an emailed statement on Tuesday. "Unfortunately, this bill and the tactics some are using to pass it would make it harder to work together – chilling debate, worsening partisanship, and setting up a false choice between voting rights and free speech. We're for both. Like the ACLU, our concerns focus on the portion that targets the First Amendment. And we'll continue to defend those rights."

A spokesman for Manchin did not return a request for comment.

Americans for Prosperity also launched a radio ad in West Virginia that quotes Manchin himself saying Democrats aren't for the Green New Deal or Medicare for All. "Encourage Senator Manchin to keep his promise. To reject a partisan agenda that will host West Virginia's back from meeting their full potential," the voiceover says in the ad.

The Koch political network is just one of many groups that have orchestrated outside efforts to oppose the Democratic-backed election bill.

The New Yorker reported on a meeting between Koch leaders and representatives from other conservative-leaning groups about how they have tried to stop the bill from passing but that some of their own polling shows the campaign finance elements of the legislation is widely supported.

Heritage Action and other groups organized a rally in March in West Virginia that was meant to pressure Manchin to oppose similar legislation to the For the People Act, , according to the watchdog group Documented.net.

Manchin has defended the Kochs from attacks by his own party.

"People want jobs. You don't beat up people. I mean, I don't agree with their politics or philosophically, but, you know, they're Americans, they're doing — paying their taxes," he said in response to questions about party leaders blasting the Kochs.

"They're not breaking the law. They're providing jobs," he said.