MADISON, Wis. (AP) -

The last time President Barack Obama came to Wisconsin to celebrate workers' rights on Labor Day, there was barely a hint of the turmoil that was to come.

Union membership has plummeted in Wisconsin over the four years since Obama last attended the labor rally in Milwaukee, thanks to the 2011 law that effectively ended collective bargaining for most public workers.

The president's appearance Monday comes as the architect of that law, Gov. Scott Walker, is locked in a tight re-election battle against Democrat Mary Burke.

Burke will also attend the event, but is not speaking. Instead, Burke will meet privately with Obama. Burke spokesman Joe Zepecki says it is not appropriate for Burke to speak at the rally Obama is attending because it is an official White House event and not a campaign rally. Zepecki says Burke has invited Obama to return for a campaign event before the election and is optimistic that will happen.

Gov. Scott Walker also won't be greeting Obama when he comes to the state. The governor's spokeswoman Laurel Patrick says Walker will be spending time with his family "before the campaign season kicks off."

Walker greeted the president in January when he came to Wisconsin.