Emails obtained by The Associated Press show Cruz campaign officials have raised questions about the 622 signatures submitted by the Kasich campaign. A minimum of 500 valid signatures is required for a presidential candidate to qualify for the Montana ballot.

The Cruz campaign asserts Kasich's petition contains signatures with invalid notaries, improper dates, mismatched phone numbers and illegible names, among other potential discrepancies.

"Because John Kasich's campaign filed only 622 signatures, and the minimum number of signatures required under Montana law is 500, there is a reasonable probability that material defects with his petitions reduce the number of valid signatures below the required minimum," the campaign said, "and John Kasich is therefore not eligible for placement on the ballot."