The Missouri House is advancing a bill to require annual written authorization from public employee union members before paying union dues.
The measure endorsed in a voice vote Wednesday would require similar approval for unions to spend worker fees on political activities.
Lawmakers exempted unions representing first responders, such as police and firefighter organizations.
Supporters say it gives workers more choice over how unions spend their dues. Opponents say it's a politically motivated attempt to weaken unions.
Democratic Gov. Jay Nixon has vetoed similar legislation.
The bill needs another vote of approval to move to the Senate.
