Rep. John Conyers (J. Scott Applewhite/AP)

Update 3:01 p.m.: Wayne County Clerk Cathy Garrett now says Conyers doesn't have the required signatures to make the Aug. 5 ballot. That is not, however, the final decision on the matter. That will come Wednesday.

Rep. John Conyers (D-Mich.), who stands to become the longest-serving member of Congress if he wins reelection this year, might not even qualify for the ballot.

According to a new report in The Detroit News, two more people who gathered signatures for Conyers are not registered voters in Michigan. Two others who were previously identified as not having been registered now appear in state records as having registered on Monday -- well after the campaign's signatures were submitted.

Michigan requires those circulating petitions to be registered voters in the state, and Conyers's primary opponent, Rev. Horace Sheffield, is challenging the signatures on those grounds.

Conyers currently has 1,193 valid signatures, according to the newspaper, and needs 1,000 to qualify for the ballot. The four aides in question collected 525 total signatures, but it's not clear how many of them are among the signatures deemed to be valid and thus could be deducted from the 1,193.

Conyers's campaign turned in 2,000 signatures overall, so on average about 60 percent of signatures are valid. If that average is also true for the four aides, that would mean 315 valid signatures would be in question -- well more than the 194 required for Sheffield to boot Conyers off the ballot.

Conyers , who has been in Congress for nearly five decades, is currently the longest-serving member of the House behind fellow Michigander Rep. John Dingell (D). Dingell is retiring this year.