Meanwhile, opponents of right-to-work laws contend they push wages and benefits lower. Michigan Democrats frequently cite a study by the liberal-leaning Economic Policy Institute reporting that employees in right-to-work states earn $1,500 less annually than their counterparts in states without such laws.
The Economic Policy Institute acknowledged it is "notoriously difficult" to evaluate the effects of a single state policy, but said its wage analysis was controlled for more than 40 different factors such as age, race and education.
The conservative Mackinac Center for Public Policy in Michigan says compensation in right-to-work states can be even higher than elsewhere when costs of living are considered. A study by the Indiana Chamber of Commerce found personal income grew more in right-to-work states than those with no right-to-work laws between 1977 and 2008.
"Very little is actually known about the impact of right-to-work laws," Gary Chaison, a professor of labor relations at Clark University in Massachusetts, said Monday. "There's a lot of assumptions that they create or destroy jobs, but the correlation is not definite."
Democrats contend the disagreement over such questions is one reason why the Legislature should allow further consideration, although Republicans say the issue is longstanding and the viewpoints clear.
"These so-called right-to-work laws, they don't have anything to do with economics, they have everything to do with politics," Obama told cheering workers Monday during a visit to an engine plant in Redford, Mich. "What they're really talking about is giving you the right to work for less money."
U.S. Sen. Carl Levin and members of the state's U.S. House delegation met with Snyder on Monday in Detroit and urged him to veto the legislation or amend it to allow a statewide referendum. Levin said the governor pledged to "seriously consider" the requests.
In Lansing, leaders of the Democratic minority in the state House acknowledged there was little they could do to stop the fast-moving legislation in the waning days of the session. However, they vowed to vote against other legislation as a form of protest, including one that helps to finance a downtown Detroit project featuring a new home for the NHL's Detroit Red Wings.
Ari Adler, spokesman for Michigan House Speaker Jase Bolger, chided those in Washington for "trying to tell Republicans in Michigan to slow down and not do our job in Lansing while they fail to resolve the nation's fiscal cliff crisis or even approve a budget."
Associated Press writers Tom LoBianco in Indianapolis, Ed White in Detroit and Ben Feller in Redford, Mich., contributed to this story.