Republican presidential candidate and Wisconsin Gov. Scott Walker made a name for himself battling public-sector unions, and now he wants to take that fight to the federal level.

During a speech in Illinois Thursday, Walker said he would take on federal employee labor groups on his first day in office. His proposal would require the unions to disclose exactly what percentage of union dues are spent on political activity, and ban the automatic deduction from feds’ paychecks in a corresponding amount.

Walker said his plan was part of an effort to “wreak havoc on Washington” by transferring “power from the big government union bosses to the hardworking taxpayer,” according to the Associated Press.

One such labor leader, American Federation of Government Employees President J. David Cox, derided the proposal, noting union dues automatically withdrawn from federal paychecks do not go to supporting federal candidates. Those contributions instead come from optional donations from union members to the group.

Walker maintained his plan, which he is scheduled to unveil in full on Monday, would stop federal employees’ money from going to politicians or political activities they do not support. Unions can use mandatory dues to pay for certain political organizing.

However, while federal employees in unions are obligated to pay dues, their memberships are entirely voluntary. Unlike at the state and local level, federal unions cannot require collective bargaining units join the group by paying dues. Federal employee unions are allowed to maintain some members who collect a federal salary and work in federal offices while spending at least part of their work days conducting union business -- a practice known as official time -- because they must represent non-union members in negotiations.

The Supreme Court will in its next session hear a case challenging any public sector union’s ability to mandate dues payment.

“Union dues are used for negotiating with management on better working conditions, protecting employees from discrimination and retaliation in the workplace, and educating lawmakers and congressional staff from both sides of the aisle on issues of vital importance to employees,” Cox said.

He added it was “no surprise” Walker would launch an attack on federal unions, given his history.

Cox called the plan “a blatant political attack on federal employees and an attempt to wipe labor unions off the map.”

National Treasury Employees Union President Tony Reardon similarly called Walker’s plan unnecessary.

“Membership in federal employee unions is totally voluntary,” Reardon said. “There is no requirement for federal workers to join a union.”

Walker’s proposal does not go as far as measures put forward in the last Congress by Sen. Tim Scott, R-S.C., and Rep. Mark Meadows, R-N.C., which would have prohibited automatic deductions for union fees altogether. Cox said at the time that if enacted, those bills would severely disrupt AFGE’s primary source of funding.

While Walker's plan would likely receive a warm reception from many in Congress, he promised to avoid taking it to lawmakers altogether with his Day 1 proposal. The feasibility of such a maneuver would likely prove difficult, as unions’ dues collection procedures are codified in statute and collective bargaining agreements.

Walker made his proposal after dropping in recent weeks from frontrunner status to far below the top tier of contenders, according to recent polls.