DETROIT—The federal judge handling Detroit's bankruptcy case gave a preliminary victory Wednesday to the city's emergency manager, ruling that municipal unions and others couldn't go to state court to litigate their grievances with the city's bid to shed its retiree obligations.

However, federal bankruptcy Judge Steven Rhodes said municipal unions, pension funds and other creditors could still argue in his court that Detroit's July 18 Chapter 9 bankruptcy filing was improper and violated Michigan's Constitution.

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