JEFFERSON CITY, Mo. -- Supporters of a right-to-work measure to ban mandatory union dues in Missouri on Monday announced lawsuits challenging ballot proposals that would undermine that policy.

The National Right to Work Foundation is helping three workers sue against ballot initiatives that would ask voters to amend the constitution to ensure union negotiating rights.

The lawsuits come as the Republican-led Legislature is moving quickly to send a right-to-work bill to Republican Gov. Eric Greitens, who supports right to work.

Missouri AFL-CIO president Mike Louis filed several versions of ballot proposals to reverse the policies in anticipation of such a bill passing.

Opponents argue in the lawsuits ballot summaries written under Democratic Secretary of State Jason Kander are too vague and misleading. Summaries are meant to help voters understand ballot initiatives.

"These deliberately misleading initiative petitions are nothing more than an attempt by Big Labor to confuse voters in hope that the confusion will result in overturning popular right-to-work protections," Mark Mix, president of the National Right to Work Foundation, said.

In an email, Louis called the lawsuits an "attempt by a dark money group" to influence state affairs. The National Right to Work Foundation is a national nonprofit organization in favor of right-to-work legislation.

"Why is a DC-based special-interest group, funded by the uber-rich, challenging the rights of hard-working Missourians to have their voices heard at the ballot box?" Louis said.

The Missouri Senate debated a right to work proposal Monday that would prohibit mandatory union fees in workplaces. An amendment proposed by Sen. Jason Holsman to put the right to work on the next election ballot was defeated.

The House voted 100-59 in favor of a similar proposal last week.