More than 12,000 workers from throughout Michigan and the U.S. Midwest either crowded into the state Capitol or marched outside on Tuesday as the Republican- majority Michigan House of Representatives approved a law prohibiting unions from compelling workers to be members and pay dues.

CNN reported that the pro-labor protesters crowded to the state Capitol in Lansing, capital of Michigan, while supporters of the right-to-work legislation were also there, although they were heavily outnumbered.

The legislation approved by the Republican-controlled Michigan House of Representatives on Tuesday covers private, and public sector unions, except for fire and police.

The right-to-work law allows workers to hold a job without being forced to join a union.

President Barack Obama voiced his opposition to the right-to- work measures during a visit to the Daimler Detroit Diesel plant in Michigan on Monday, saying efforts to pass such measures were not about economics but about politics.

The right-to-work movement has been growing in the United States in recent years. Indiana earlier this year became the first state in the industrial Midwest to approve it.

Michigan is the 24th state to enact right-to-work bills.

Michigan is home of the heavily unionized U.S. auto industry, with some 700 manufacturing plants in the state. It is also the birthplace of the United Auto Workers, the richest U.S. labor union. Michigan ranked fifth in the U.S. in terms of the percentage of unionized workers, at 17.5 percent.