MADISON, Wis. — A political action committee with close ties to Gov. Scott Walker has launched a $575,000 television advertising campaign to benefit Republican U.S. Senate candidate Leah Vukmir (VOOK'-meer).

The Wisconsin Next PAC says its ad released Thursday is running statewide in April, on top of $225,000 spent on digital and radio ads.

It touts Vukmir as a "proven conservative." She faces Delafield businessman Kevin Nicholson, a former Democrat, in the Aug. 14 Republican primary.

The TV spot also credits Vukmir with leading the fight to pass Walker's Act 10 law in 2011 that effectively ended collective bargaining for public works. The ad calls opponents who protested against it "union thugs" who tried to "bully Wisconsin conservatives."

Walker is not officially endorsing in the race, but his wife Tonette Walker backs Vukmir and their son works for her campaign.