Last Updated May 23, 2014 5:00 PM EDT
DETROIT - A judge on Friday ordered U.S. Rep. John Conyers to be placed on the August primary ballot, overturning a decision by Michigan election officials who found the Detroit Democrat ineligible because of problems with his nominating petitions.
Many petitions were thrown out because the people who gathered signatures weren't registered voters or listed a wrong registration address. That put Conyers more than 400 short of the 1,000 needed to run for re-election.
But U.S. District Judge Matthew Leitman issued an injunction reinstating Conyers, two days after hearing arguments from the American Civil Liberties Union and Conyers' lawyer challenging Michigan's law.
They said the law that puts requirements on people gathering petition signatures is unconstitutional, noting that a similar law in Ohio was struck down by a federal appeals court in 2008.
The Michigan attorney general's office had urged Leitman to reject Conyers' challenge. In defending the law, the state said Conyers had followed the requirements for years.
"Any midstream changes are confusing to candidates and voters alike," Assistant Attorney General Erik Grill said. "And such a change is unfair to candidates who have already followed the challenged law and complied with its registration requirement."
Conyers, 85, has been in Congress since 1965 and would be the longest-serving member of the House if re-elected.
He has routinely won re-election - often with more than 80 percent of the vote - and became the senior member of the Congressional Black Caucus, which he helped found. He won in in 2012 with 83 percent.
In 2012, another Michigan congressman, Republican Thad McCotter of suburban Detroit, didn't make the ballot because a staff member turned in phony signatures or ones from old petitions. McCotter announced he would mount a write-in campaign but later dropped the effort.
The most important national case of a successful write-in campaign was in 2010, when Alaska Republican Sen. Lisa Murkowski won re-election using that method after she was defeated by a tea party candidate in the Republican primary.