Labor leaders point to Snyder and Walker as their prime targets in the 2014 elections. However, Walker is seen as having the upper hand in light of his win last summer in the highly publicized recall election.
Walker raised more than $30 million to beat Democrat Tom Barrett in the June recall by almost 7 percentage points, a wider margin than their first face-off in the November 2010 election.
"Gov. Walker is a national figure now and has already faced down a direct challenge from labor, a benefit he did not have in 2010," said Walker adviser Dan Blum.
The AFL-CIO's Podhorzer said unions also plan to target Ohio Gov. John Kasich, who was seen as weakened when his enactment of a measure limiting public employee bargaining rights was overturned by referendum. Kasich's approval in surveys of Ohioans has improved somewhat, although it remains below 50 percent.
Hungry for a win, unions also are circling Corbett in Pennsylvania and Florida Gov. Rick Scott. Though the states are expensive for advertising, the Republican governors are seen as vulnerable, with approval ratings below 40 percent in November.
While defeating Corbett, Kasich, Snyder or Walker would strike a blow for more traditionally pro-labor manufacturing states, the chance to defeat Scott is seen as a potential bright spot for labor's future.
"Florida is different. It's one place where unions are trying to expand," said Florida Democratic strategist Steve Schale.
Florida is a weak labor state, but one where the heavy presence of service-sector jobs gives large and newer unions such as Service Employees International Union an opportunity to grow.
Former Gov. Charlie Crist, who left the Republican party and has changed his affiliation to Democrat, is eyeing a run for governor in 2014. Crist was seen as a defender of public-sector unions.
Conservative groups deny claims that the push for right-to-work laws and other anti-union measures is part of a concerted GOP effort to weaken unions because they are a pillar of Democratic candidates and causes.
"It means that Michigan is going to be more prosperous and workers there are going to have more freedom and choice when it comes to a union," said Tim Phillips, president of Americans for Prosperity, which has funded anti-union measures in Michigan and around the country.
But Phillips said the decrease in union membership "does impair their ability to just bully people politically, which they've done for a long time."
Beaumont contributed from Des Moines, Iowa.
Follow Sam Hananel on Twitter: http://twitter.com/SamHananelAP
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