JEFFERSON CITY, Mo. (AP) - Republican Gov. Eric Greitens has made Missouri the 28th state to ban mandatory union fees.

Greitens signed the right-to-work bill into law Monday. He's spending the day traveling around the state announcing his support for the measure.

At his last stop, in Jefferson City, the governor stood with dozens of Republican lawmakers at the state capitol.

“Today, passing right to work sends a very clear message. That the people of Missouri are ready to work — and Missouri is open for business,” he said.

The governor had pledged to sign right to work while on the campaign trail. He and other supporters say it will bring business and jobs to the state. Opponents say it aims to weaken unions and could lead to lower wages.

“Right to Work is a simple and a straight-forward measure. What right to work simply says is every worker in the state of Missouri has a choice, to decide for themselves, whether or not they want to join a union. And if they choose not to join — they can’t be forced out of their job,” Greitens added.

“Right to work doesn’t eliminate unions, it makes them more responsible and accountable to their members on the front lines.”

While right-to-work advocates celebrated a victory, union leadership promised to keep fighting.

"Our next step is we feel that this is serious government overreach,” said Pat White, President of the St. Louis Labor Council. “And our members along with other people in the state of Missouri, feel that they should be heard on this, so we're hoping to put it on the ballot within the next couple of years and let the people decide."

Seven of the eight states that surround Missouri already have right-to-work laws, including Kentucky where it passed last month. New Hampshire lawmakers are considering a similar proposal.

Missouri's new law will take effect Aug. 28. It exempts contracts in place before then until they expire or are reopened.

WATCH: What does 'right-to-work' mean for Union members