LANSING, Mich. (AP) — Fraudulent signatures could upend Michigan’s congressional races this year as each declared GOP U.S. Senate candidate faces new calls to investigate their attempts to get on the August primary ballot and a Democratic U.S. House candidate appears likely to fall short.

Just two years ago, multiple high-profile gubernatorial campaigns fell into the same trap and lost access to the ballot.

Adam Hollier, a former state senator who has garnered significant Democratic support in his primary challenge of U.S. Rep. Shri Thanedar, is expected to be kept off the August primary ballot after county election staff found he did not have enough valid signatures on nominating petitions.

Republicans vying for Michigan’s open U.S. Senate seat are now facing similar allegations after state and national Democratic groups submitted a request that their nominating petitions be investigated on Friday.

The Michigan Democratic Party and Democratic Senatorial Campaign Committee alleged in a letter sent to the Michigan Board of State Canvassers that the signatures on the petitions of each of the Republican Senate candidates show “patterns that indicate the presence of potential forgery and other fraudulent signature gathering tactics.”

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Senate candidates in Michigan had to submit 15,000 valid signatures by April 23 to qualify for the August primary election. Michigan election law provides a seven-day window for challenges to these signatures. Although the Democratic groups missed this deadline, they have requested the state canvassing board to open an investigation, which is permitted under Michigan election law.

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The petitions are worthy of investigation, according to the letter, because they show signs of “a possible repeat of the conduct of petition circulators during the 2022 election.”

Five Republicans running for governor in 2022 were kept off the ballot after fraudulent signatures were found on their nominating petitions. Three people have been charged with forgery and other crimes related to the phony petition signatures but no candidate was personally accused of knowingly submitting fraudulent petitions.

Michigan’s U.S. Senate race is one of the most hotly contested in the nation after longtime Democratic Sen. Debbie Stabenow announced that she would retire this year, leaving the battleground seat open in a year when each party is fighting for control of the upper chamber.

Former U.S. Reps. Mike Rogers and Justin Amash, along with businessman Sandy Pensler, are vying for the Republican nomination but all face allegations of fraudulent signatures from the Democratic groups. Rogers, the Republican frontrunner, has submitted the maximum allowed 30,000 signatures. For him not to qualify, half of those would need to be deemed invalid.

In a statement, Pensler expressed confidence that he would qualify for the ballot after turning in 26,000 signatures and said that “Democrats can’t beat Republicans at the ballot box so it looks like they are trying to eliminate Republicans from the ballot.”

A request for comment sent to Amash’s campaign was not immediately answered and Rogers’ campaign did not provide a statement in time for publication.

In the race for Detroit’s U.S. House seat, Hollier was perceived as the biggest threat to Thanedar winning a second term in office, racking up endorsements from several prominent Michigan Democrats including Secretary of State Jocelyn Benson and the leadership of the Black Congressional Caucus.

Thanedar challenged Hollier’s signatures earlier this month and a report by the Wayne County Clerk’s Office made public Thursday deemed that Hollier did not have enough valid signatures. Wayne County Clerk Cathy Garrett is expected to make a determination in the coming days of whether Hollier will be on the ballot or not.

“This is voter suppression by any other name. We are in the process of carefully reviewing our next steps and will have more to say shortly,” said Hollier’s attorney, Melvin Butch Hollowell.

Hollier had submitted 1,550 signatures to meet the ballot requirement, surpassing the 1,000 needed, but later said that some signatures showed “evidence of fraudulent signatures” and that the “fraudulent activity was not conducted at the direction” of the campaign.

The campaign is forwarding the fraudulent signatures “to the proper authorities for additional investigation,” according to a statement.