Rep. John Conyers has served in Congress for nearly a half century - but a county election official ruled today that he failed to submit enough valid signatures to appear on the Michigan Democratic primary ballot in August.

"It is my determination that in accordance with the current laws and statutes of the State of Michigan, the nominating petitions filed by Congressman John Conyers, Jr. are insufficient to allow his name to appear on the August 5, 2014 Primary Ballot," Wayne County Clerk Cathy Garrett said in a statement.

Conyers is challenging the decision, a Democratic strategist working with his campaign told ABC News, but if the challenge fails, he will have to run as a write-in.

If he would win the primary as a write-in candidate, his name would be on the ballot for the general election.

Conyers is seeking a 26th term in the House.

Rep. Steve Israel, chairman of the Democratic Congressional Campaign Committee, downplayed the ballot challenge. "The DCCC fully supports Representative Conyers in his re-election campaign, and I have every confidence that when this long process is complete, Representative Conyers will continue to serve the people of Michigan in Congress," Israel said in a statement. "As the next Dean of the House, the Michigan delegation and pillar of the Democratic party, Representative Conyers will remain one of the most respected voices in Congress," he said.

Election officials in Michigan said two of the people who were gathering signatures for his name to be on the ballot were not registered voters, so the 1,000 signatures they gathered were disqualified.

The ACLU filed a suit in federal court Monday, saying it was unconstitutional to require people to be registered voters to gather signatures.

While his district is a safe Democratic seat, party officials say the episode is an embarrassment for the congressman, who will turn 85 on Friday. But with such high name recognition in the Detroit area, a write-in campaign is an obstacle, but likely not a roadblock to winning another term.