A 20-year campaign by rightwing billionaire donors to undermine trade unions and strike a blow at the progressive movement in America comes to a climax on Monday, in a hearing at the U.S. Supreme Court.

The nine justices of the nation’s highest court will hear arguments in Janus v. AFSCME, a case that has the potential to strip unions of a major source of income. Should the court rule against the public sector unions – as many fear it will – they stand to suffer a decline in their 7.2 million-strong membership, and with it the withering of their political strength.

Conservative activists and thinktanks, backed by corporate donors including the Koch brothers and the Bradley Foundation, have long been preparing for this moment, as part of a larger campaign to tilt the democratic process to the right. In just the past four years, the supreme court has considered three challenges to public sector unions.

“The supreme court this time appears to be poised to knock the legs from under union advocacy, in what would be a major victory for the rightwing jurisprudential movement,” said Dan Weiner, senior counsel at the Brennan Center for Justice, a nonpartisan group.

A Guardian review of public records shows that the Bradley Foundation, a Wisconsin-based mega-donor to rightwing causes, has invested heavily in the anti-union campaign. Since the 1990s, the donor has given $30.5 million to 24 conservative groups that have supported the legal assaults against public sector unions that have reached the supreme court. The two sponsors of the Janus case, the National Right to Work Legal Defense Foundation and the Illinois Policy Institute’s Liberty Justice Center, have between them received $1.6 million in Bradley donations since 2003.

The Bradley Foundation was created in 1986 as a way of using the vast manufacturing wealth of two brothers, Lynde and Harry Bradley, to advance “the principles and institutions of American exceptionalism.” Though constituted as a tax-exempt, nonprofit entity, private correspondence reveals a frank exchange about the hyper-partisan and blatantly political ambitions it has for its $900m “charitable” reserves.

Documents stolen from the foundation in 2016 by international hackers, and released to the public by the Center for Media and Democracy and the Milwaukee Journal Sentinel, laid bare the organization’s ideological thinking. The documents show that Bradley donated to the National Right to Work Foundation, sponsor of the Janus case, because “Big Labor and trial attorneys are the two principal funding pillars of the left.”

Minutes of a Bradley committee meeting in February 2016 reveal the foundation’s estimate of what restricting union rights would do in just four of the most unionized states, New York, California, Oregon and Washington. They calculated that some 2.8 million public employees would be affected, with more than $2 billion of union income at stake.

The minutes go on to make plain the greater political purpose: “The largesse of Pacific Coast unions, after redistributed [sic] out of national offices in Washington, D.C., is used to subsidize the Left’s national agenda and obstruct the mission and program interests of the Bradley Foundation and its allies.”

The mission statement echoes the campaign launched last year by the State Policy Network, another Bradley recipient, that aimed to “defund and defang” public sector unions.

The idea that draining power from unions can enervate other progressive movements is not an idle one. A recent from the National Bureau of Economic Research found that right-to-work laws that limit unions at state level, in much the same way that the Janus lawsuit would do nationally, have suppressed the Democratic party’s share of the presidential vote by 3.5%.

Lee Saunders, president of the AFSCME, the nation’s largest public employee union and the defendant in Monday’s Janus case, said the intention behind the legal action was to gut the power of progressive forces. “The billionaires and corporate special interests behind this case don’t believe we should have a seat at the table,” he said.

Randi Weingarten, president of the American Federation of Teachers, said the Bradley Foundation’s aim was to create “a monopoly on economic and political power. They want the playing field entirely to themselves.”

In Wisconsin, Weingarten said, the Foundation was a key backer of Scott Walker. Bradley’s president in 201 was Michael Grebe, who served as Walker’s campaign chairman when he for the governorship that year. Since Walker introduced Act 10, a measure to block collective bargaining for public sector workers, overall union membership has fallen from 14% to 9% in the state, with similar steep declines in pay and benefits.

At the heart of the Janus case is whether trade unions can legitimately charge all public employees a portion of the costs of collective bargaining, on grounds that every worker, and not just union members, benefits from negotiated higher wages. Such “fair-share” fees are currently allowed in 23 states, and were approved by the US supreme court in 1977 in Abood v. Detroit Board of Education.

Rightwing groups, funded by the Bradley Foundation and other major donors, see such fees as a pillar of union strength and have been stepping up attacks on them in recent years. In 2016 the US supreme court appeared to be on the verge of knocking down “fair-share” fees in the case Friedrichs v. California Teachers Association. Conservative justice Antonin Scalia died before a ruling, leaving the court at a 4-4 draw.

The renewed anti-union assault appears to have good prospects of success, with a ruling expected by June. Monday’s suit, brought by an Illinois child support worker named Mark Janus, argues that his first amendment free speech rights are violated by having to contribute fees to a union which he does not support. The case will be one of the first decisive outings for Neil Gorsuch, the conservative justice picked by Donald Trump to replace Scalia on the court.

Gorsuch’s outspoken conservative beliefs have riled some court observers. On the same day last September that the supreme court agreed to hear the Janus case, Gorsuch gave a speech at the Trump International Hotel in Washington, at an event hosted by a conservative group whose funding comes from the Bradley Foundation, among other donors.

Rick Graber, president of the Bradley Foundation, said that it was backing the Janus suit as part of a wider commitment to First Amendment rights, and to “ensure that America remains a land of freedom, equality and opportunity.” He denied that the foundation had stepped beyond its charitable status to engage in direct partisan politics.

“The Foundation only gives to nonprofit organizations that are in line with its mission,” he said, “to foster strong families and communities, inform and educate citizens, advance economic growth, and encourage individuals to become self-reliant rather than turn to a government agency to solve problems.”

Originally published by The Guardian