Rightwing activists across the US have launched a nationwide campaign to undermine progressive politicians by depriving them of a major source of support and funding – public sector unions.

A network of conservative thinktanks with outposts in all 50 states has embarked on a “breakthrough” campaign designed to strike a “mortal blow” against the American left. The aim is to “defund and defang” unions representing government employees as the first step towards ensuring the permanent collapse of progressive politics.

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The campaign carries a powerful echo of the populist creed espoused by Donald Trump. The president was propelled into the White House last November after unexpected victories in several previously Democratic rust belt states including Michigan and Wisconsin, both of which have endured withering attacks on trade unions in recent years.

The new assault is being spearheaded by the State Policy Network (SPN), an alliance of 66 state-based thinktanks, or “ideas factories” as it calls them, with a combined annual budget of $80m. As suggested by its slogan – “State solutions. National impact” – the group outlines an aim to construct a rightwing hegemony throughout the US, working from the bottom up.

To do that, it first has to sweep aside the public sector unions and their historic ties to Democratic and progressive politicians. In a 10-page fundraising letter, part of a set of documents obtained by the Center for Media and Democracy and published by the Guardian today for the first time, SPN sets out its mission in frank language that does not disguise its partisan ambitions.

The author of the letter, SPN’s president and CEO Tracie Sharp,describes the $8m “breakthrough” campaign as a “once-in-a-lifetime chance to reverse the failed policies of the American left … We are primed, right now, to deliver the mortal blow to permanently break its stranglehold on our society.”

Sharp pitches the battle against unions as the start of a war on progressive politics, with the ultimate goal of winning elections for rightwing candidates. “Big government unions are the biggest sources of funding and political muscle for the left – and a major obstacle to the ability of voters to reclaim control of American government. To win the battle for freedom, we must take the fight to the unions, state by state.”

The target of such union-bashing, she openly admits, is to “defund and defang one of our freedom movement’s most powerful opponents, the government unions”. The long-term objective is to “deal a major blow to the left’s ability to control government at the state and national levels. I’m talking about permanently depriving the left from access to millions of dollars in dues extracted from unwilling union members every election cycle” (emphasis in original).

SPN will be discussing its anti-union and anti-left agenda on Wednesday at its annual meeting in San Antonio, Texas. Its morning session will look at how “labor reform” can be pursued with renewed vigor under the Trump administration.

The discussion will feature some of the key architects of SPN’s political strategy, including Vincent Vernuccio who pioneered anti-union legislation in Michigan, and Tom McCabe of the Freedom Foundation, who has sent his foot soldiers on an aggressive offensive against collective bargaining in the US north-west.

Mary Bottari, deputy director of the Center for Media and Democracy (CMD) which tracks the rise of rightwing groups in America, said the fundraising letter and other SPN documents published by the Guardian cast light on the conservative game plan. “It’s very rare to catch conservative thinktanks talking so openly and blatantly about their long-term political aims. These documents reveal to us that SPN’s goals are entirely political – they have no concern for workers or union members, their only goal is winning elections to advance rightwing causes.”

Bottari added: “An $80m campaign to ‘defund and defang’ public sector unions is remarkable, both in its size and in its ambition.”

Public sector unions have come under growing fire from conservatives in recent years. While unions operating in private companies have been diminished since the 1980s – their membership plummeting from about 17% of the workforce in 1983 to just 6% today – their equivalents in the public sector such as teacher, local government, police and fire officer unions have remained relatively stable, at around 35%.

But in 2010, Scott Walker, the newly elected governor of Wisconsin, opened a new front in America’s partisan war when he passed Act 10, stripping public sector unions of the power to bargain collectively and forcing them to re-certify themselves every year with electoral backing from more than 50% of all workers, not just those voting. The move has spawned a rash of imitations across Republican-controlled states, with Iowa and Indiana passing similar laws, and a further 15 states introducing legislation – encouraged by SPN, which has framed a model bill to make it easier for Republican legislators to adopt the changes.

A total of 28 states have also passed “right to work” laws that allow workers in private companies to refuse to join unions despite enjoying the fruits of collective bargaining.

Though the long-term consequences of such union restrictions have yet to be fully understood, there are early indications that the impact could be profound even at presidential level. Since Act 10 came into effect in Wisconsin, public sector union membership has slumped by 40%, or about 136,000 people.

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Trump won Wisconsin last November by just 23,000 votes.

A similar pattern can be seen in Michigan where unions have shrunk steadily since a right-to-work law came into effect in 2013, with a loss of at least 30,000 members. Trump took Michigan, to the shock of Hillary Clinton and her supporters, by just 11,000 votes.

When asked whether anti-union laws in Michigan and Wisconsin had affected the outcome of the presidential race, Matt Patterson of the conservative group Americans for Tax Reform said: “No question in my mind. Hard to fight when your bazooka’s been replaced by a squirt gun.”

Carrie Conko, SPN’s vice president of communications, said that the network does not involve itself in political campaigns. “Labor reform is an issue where SPN has been clearly on the side of workers who are against forced unionization and the use of their hard-earned wages to support causes they don’t believe in. If workers choose to support their unions agenda that is fine – but, right now, in many states they don’t have a choice or a voice.”

Conko’s statement echoed the language used in an SPN “toolkit”, also published here for the first time, that advises Republican policymakers on how to campaign for anti-union legislation. “Be pro-worker, not anti-union,” the pamphlet says. “Frame union reform from the point of view of the members and how the reform helps them have a greater voice in their union. Don’t rant against unions. We’ve all been frustrated by the actions of public sector unions to block pro-freedom reforms, but publicly venting these feelings is counterproductive.”

SPN’s disclosure of its political and partisan objectives in the new documents could arouse the interest of investigators from the Internal Revenue Service. The group is constituted as a 501(c)(3) organisation, which renders it exempt as a charity from taxation.

Marc Owens, a partner with Loeb & Loeb who worked as an IRS lawyer specializing in charitable tax exemptions, said that the provision was designed for charitable purposes, not for lobbying against public sector unions or for activities to influence the outcome of elections. “A charity that does those things is not engaging in charitable activities and that puts its tax exempt status in jeopardy,” he said.

Conko told the Guardian that SPN takes “great care to be fully in compliance with all applicable laws and regulations”.