WASHINGTON (AP) – The legal fight over Colorado’s U.S. Senate race took another turn Monday as two Republican candidates each challenged a decision by state officials that would bar them from the June 28 primary.

Colorado’s Secretary of State ruled last week that Senate hopefuls Robert Blaha and Ryan Frazier failed to gather enough signatures to qualify for the GOP primary and a chance to unseat Sen. Michael Bennet, the Democratic incumbent.

State election rules require that Senate candidates looking to make the ballot through the signature or “petition” process must gather 1,500 or more signatures from each of Colorado’s seven congressional districts – or at least 10,500 overall.

Blaha, a wealthy businessman, fell short in three districts and Frazier, a former Aurora city councilman, missed the mark in four districts.

In court filings, Blaha argued that hundreds of signatures were rendered invalid because of small record-keeping errors, such as a mismatch between the home addresses listed by aides who collected signatures and the home addresses that the state had in its voter registration record.

“Thousands of Coloradans expressed an interest in seeing Robert Blaha on the ballot this June, and their voices should be heard,” said Katey Price, a Blaha spokeswoman, in a statement.

Frazier made a similar argument in his appeal.

Presently on the ballot: Darryl Glenn, an El Paso County Commissioner; Jack Graham, the former athletic director of Colorado State University; and Jon Keyser, a former state lawmaker.

Glenn earned a spot at the state Republican convention. Graham and Keyser both qualified by petition – though Keyser had a bumpier ride.

Colorado’s secretary of state originally declared that Keyser had fallen short in one congressional district.

Keyser appealed and argued that state officials unfairly threw out dozens of signatures. A judge sided with Keyser because – in spite of the error – his campaign had “ substantially complied” with the law and there was no evidence of fraud.