Two of the six Montana Republicans who have filed to challenge Democratic Sen. Jon Tester in next year's race have failed to complete a public financial disclosure report as required by law, including former judge Russell Fagg, according to the U.S. Senate website.

Fagg filed to run for Tester's seat in the U.S. Senate on Oct. 18. Federal law gives candidates 30 days to file a financial disclosure after becoming a candidate for office. Fagg and Republican candidate Al Olszewski have not done so; nor have they applied for extensions.

Fagg didn't respond to requests for comment on Monday.

Earlier this year, the American Democracy Legal Fund filed a federal complaint against the former Yellowstone County district judge, alleging he violated campaign finance laws that included campaigning for the Senate without filing for the seat.

That complaint remains before the Federal Election Commission and Fagg has said he will fight the accusations. Opponents, however, say he continues to run a shadowy campaign, as evidenced by his failure to complete a public disclosure of his finances.

Such disclosures typically note the candidate's business interests, sources of income, financial assets and liabilities. By law, a candidate who files a report more than 30 days after it's due without having received an extension must pay a $200 penalty for late filing.

According to the latest campaign finance reports on file with the Center for Responsive Politics, as of September, Tester has raised more than $7.6 million in his reelection bid and has spent more than $2.3 million.

Of the four Republican challengers who filed a public financial disclosure report, Troy Downing has raised the most at $492,000 while spending $185,000. He's followed by Matt Rosendale, who has raised $415,000 and spent just $65,000.

Republican challenger Al Olszewski has raised $168,000 while Ronald Murray has raised $1,455.

Two Democratic challengers seeking Tester's seat have yet to file a financial disclosure, including Sarah Dean – the wife of Republican challenger James Dean – and Greg Strandberg.