ST. LOUIS — After more than a year of back and forth, voters made the final decision on so-called "Right-to-Work" legislation Tuesday, shooting the ballot measure down.

Voters rejected the measure by a wide margin, and The Associated Press called the election around 9:45.

Related: Track live results here

On all primary ballots, voters got the chance to vote on Proposition A. If passed, the proposition would adopt Senate Bill 19, also known as "Right to Work", which was passed by the Missouri general assembly in 2017 and signed by Former Governor Eric Greitens. The bill would prohibit mandatory union dues as a condition of employment in a labor organization.

The vote Tuesday marked a major victory for unions, which poured millions of dollars into a campaign to defeat Proposition A.

The right-to-work law originally was enacted in 2017 by Missouri's Republican-led Legislature and governor. But it never took effect, because unions gathered enough petition signatures to force a public referendum on it.

Unions argued the measure would have led to lower wages, while business groups claimed it could have led to more jobs. Economic studies showed mixed and sometimes conflicting results.

Although the bill was signed into law, opponents put the brakes on it and collected enough signatures to get it on the ballot.

It's a vote that's being watched around the country. It's been called "ground zero" in the right-to-work fight. Political analysts, including our Dave Robertson, say if unions here in Missouri can overturn 'Right-to-Work', supporters in other states may try to do the same.

Robertson said if Prop A had passed, it will be a big blow for unions. A punch that would be felt throughout the nation.

The Associated Press contributed to this story.