Union hits Romney on auto bailout in Ohio

The ad also quotes Romney saying in interviews "Let Detroit go bankrupt. Don't just write them checks."

Democrats and labor groups have sharply criticized Romney for opposing the federal government giving loans to General Motors and Chrysler when they were on the verge of bankruptcy during the economic panic of 2008. The federal government loaned about $80 billion to the company in a series of controversial bailouts than began under former President George W. Bush and continued under President Obama.

The auto bailout has emerged as a central campaign issue because the race for the Republican nomination has turned to Michigan, which is holding its primary Tuesday. Democrats have argued that the auto bailouts would be a political winner for Obama not just in Michigan, but in other Midwestern states with a heavy concentration of auto part supply companies like Ohio.

Romney has defended his position on the auto bailouts, writing an op-ed in the Detroit News arguing the auto companies could have survived with a "managed bailout" using private-sector capital.

“The president tells us that without his intervention things in Detroit would be worse,” Romney wrote. “I believe that without his intervention things there would be better."

Romney and other critics of the auto bailouts have noted that the federal government has not received back all of the nearly $50 billion it lent to General Motors. Additionally, the government still owns a percentage of the company's shares, leading some conservatives to mockingly refer to GM as "Government Motors."