A union steel worker holds up a sign during a rally outside the Capitol in Lansing, Mich., on Dec. 6, 2012. (Carlos Osorio/AP)

Michigan union activists are protesting outside the Capitol in Lansing as controversial "right to work" legislation becomes law.

Police are expecting up to 30,000 protesters, including both union opponents and "right to work" defenders, the Detroit News reports. The Republican-controlled legislature is expected to reconcile their two versions of the union limits today and send a bill to Gov. Rick Snyder (R).

Access to the building is being limited, police say, to avoid a repeat of last Thursday, when protesters tried to rush the state Senate chamber and were pepper-sprayed.

The legislation would effectively ban unions in the state from requiring workers to pay dues. For the past two years, Snyder has argued that the union limits, adopted by Republicans in many other states, were too divisive in Michigan. Last week he abruptly reversed course.

Supporters of the legislation say Republicans were provoked by a failed union attempt to guarantee collective bargaining rights in the state constitution. Critics allege that Republicans are being controlled by anti-union out-of-state interests, in particular the billionaires Charles and David Koch. 

Today's events could set the stage for an ongoing battle like the one we saw in Wisconsin over the past two years. United Auto Workers President Bob King has said that should the legislation pass, the union would pursue options to recall state legislators and, perhaps, Snyder. 

In Wisconsin, two Republican state senators were forced out by union-backed recalls in the summer of 2011 after passing legislation curtailing collective bargaining rights. Gov. Scott Walker (R) beat back a recall attempt earlier this year. 

“If this bill is signed today, it will be Thunderdome for Governor Snyder and Michigan for the next two years," said one high-ranking labor official. "This fight is far from over." 

Republicans tacked a spending measure onto the legislation so that it cannot be overturned by referendum. But opponents believe they can gather enough petitions to put the law to a vote in 2014. 

President Obama spoke out against the bill Monday during a trip to a Detroit suburb, saying it was about “giving you the right to work for less money." 

Read more on this story from the Washington Post:

The Fix: The Michigan right-to-work battle, explained

Obama takes push for higher taxes on wealthy to workers at Michigan plant