DETROIT— Some Detroit retirees were sent erroneous ballots this month for voting on the city’s plan to deal with $18 billion of debt, including public pensions and exiting bankruptcy, attorneys disclosed in federal court on Wednesday.

About 2,000 of the ballots sent to members of the city’s general retirement system contained errors, lawyers said.

Carole Neville, an attorney representing a court-appointed committee for Detroit retirees, said new ballots needed to go out to these retirees as soon as possible.

The news appeared to rattle Judge Steven Rhodes, who has set a brisk schedule for Detroit’s municipal bankruptcy – the biggest in U.S. history – which was filed in July 2013. He demanded to know by Friday who was responsible for the ballot mess.

Thousands of Detroit creditors must vote and return their ballots by July 11.

It was unclear if the ballot mix-up and another problem that was discussed earlier in the court hearing would push back the start of a July 24 hearing to determine if Detroit’s debt adjustment plan is fair and feasible.

Martha Kopacz, a senior managing director at Phoenix Management Services, who in April was selected by Rhodes as the court’s expert witness to determine if the city’s debt adjustment plan was feasible, needs another week or two to complete her work, her attorney told Rhodes at Wednesday’s hearing.

Stephen Lerner, an attorney at Squire Sanders, sent the judge a letter last week that said Kopacz has not received sufficient documentation from the city to render an opinion on the plan’s feasibility by June 24, a month before the scheduled hearing.