JEFFERSON CITY, Mo. — An Illinois megadonor is contributing $500,000 to the effort to make Missouri a right-to-work state.

The St. Louis Post-Dispatch reports that Richard Uihlein donated the money Tuesday to a political action committee named “Freedom to Work.” It’s raising cash to fend off a union-led attempt to kill efforts to change state labor laws.

Last year, lawmakers passed a right-to-work law barring mandatory union fees in workplace contracts. But labor unions gathered enough petition signatures to put the law on hold until a statewide referendum can be held in 2018.

Uihlein is a wealthy packaging company executive from Lake Forest who also donated to Attorney General Josh Hawley’s bid for the U.S. Senate. Uihlein also contributed $360,000 to Gov. Eric Greitens’ maiden bid for statewide office in 2016.