Missouri became the 28th US state Monday to adopt so-called right to work legislation, whereby employees can no longer be required to pay dues to a labor union, yet are still able to benefit from any deals procured by such a union.

Newly elected Republican Gov. Eric Greitens, who assumed office last month, had campaigned in part on a promise to ensure the law came into being. His predecessor, a Democrat, had opposed the move.

The adoption of a right-to-work law by Missouri is the latest episode in a nationwide struggle between advocates of the right-to-work movement (mostly Republicans) and those who oppose it (mostly Democrats), though analysts say it is difficult to provide conclusive evidence in support of either side.

In celebration of the development in Missouri, Governor Greitens tweeted that the state is “now open for business, & Missourians are ready to work!”

Indeed, it is this very idea – that right-to-work legislation demonstrates a warm welcome for business – that lies at the heart of proponents’ arguments. More specifically, goes the thinking, such a business-friendly climate will attract more jobs and boost economic growth.

Critics counter that the drop in revenue for the unions will strip them of their ability to fight for workers’ rights, inevitably watering down the benefits and the levels of pay that a state’s workers enjoy. In short, while the state’s economy may grow, the plight of the individual may grow worse.

Studies of whether right-to-work (RTW) states do indeed attract more investment, and, conversely, whether they see wages and benefits diminished, have been inconclusive.

“Some studies find RTW boosts job growth, while other studies do not,” writes Timothy Bartik, who is a senior economist at the Upjohn Institute for Employment Research in Kalamazoo, Mich. “Some studies find RTW reduces wages, while other studies do not.”

"What seems clear," Mark Trumbull wrote for The Christian Science Monitor in early 2015, just as Wisconsin was heading toward RTW status, "is that the volume and tone of the debate over right-to-work laws far outstrips actual certainty about the impact."

Moreover, even when studies do appear to show distinct correlation between RTW legislation and either positive or negative effects, there are so many other economic and demographic factors wrapped up in the state's business data that it is challenging to draw definitive conclusions regarding causation.

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“Right to work doesn’t seem to have much of an impact one way or another,” Jake Rosenfeld, a sociology professor at Washington University in St. Louis, told the St. Louis Post-Dispatch last week, “both in improving the state’s business climate or in terms of devastating the health of organized labor.”

This report includes material from Reuters.