(Reuters) - The campaign to repeal a Michigan law that allows the state to overrule local elected officials and union contracts moved to the Michigan Supreme Court on Wednesday, with arguments centered on a technicality - font size.

The key question weighed by justices, who gave no indication when they will rule, was if the type size used on petitions seeking to overturn the year-old emergency manager law complied with state requirements.

Opponents of the law want a referendum on it to be placed on the November 2012 ballot. Stand Up for Democracy, a union-backed group, collected enough valid signatures on the petitions to qualify the measure for the ballot.

An attorney for the group argued on Wednesday that the type size used met state requirements and that it has a constitutional right to access the ballot.

A state appeals court panel ruled in June that the measure should be placed before voters.

But Citizens for Fiscal Responsibility, a business-backed group, asked the Michigan Supreme Court to overturn that ruling and obtained a motion for immediate consideration by the court earlier this month.

State election officials have until September 7 to certify measures for the November 6 ballot.

Michigan replaced its previous emergency financial manager law for troubled cities and school districts in 2011. The new law, known as Public Act 4, gave the state more power to intervene in financially strapped local governments and school districts. State-appointed emergency managers who run the governments and schools could now void collective bargaining agreements.

Parts of an April financial stability agreement between Detroit and Michigan depend on the law, which would be suspended if the repeal makes the ballot. Michigan's attorney general has said that a former, weaker emergency manager law would take its place in the interim.

Four Michigan cities and three school districts have emergency managers.

Wall Street credit rating agencies have raised concerns about the potential suspension of the law. Moody's Investors Service in March said such a move would hurt the credit quality of local governments under state oversight, including Detroit.

In a filing with the supreme court last week, Michigan's Secretary of State said if the court rules the actual letters should be measured to determine type size, that decision would "most certainly" invalidate six other measures awaiting certification for the ballot.

Those measures include proposed constitutional amendments designating collective bargaining as a right, authorizing eight new casinos, requiring voter approval for a new international bridge crossing, and mandating voter approval or a two-thirds vote by the Michigan Legislature for new or additional taxes.

(Reporting by Karen Pierog; Editing by Richard Chang)