For the first time in more than two decades, Arizonans won't have the option to vote for a Libertarian Party candidate for governor.

A 2015 law makes it much harder for candidates of minor parties to actually get their names on the general election ballot, whether through petitions or write-in votes.

Prior to 2015, candidates for minor parties could get on the ballot simply by submitting petitions with the signatures of one-half of one percent of those registered with the party. 

The law actually lowers the requirement to one-quarter of one percent, but it adds political independents to the base, who actually outnumber Democrats and run a close second to Republicans.

So this year the minimum signature requirement for a Libertarian running statewide was 3,153 — about 10 percent of all those actually registered as Libertarians. If the 2015 law had not passed they would have only needed about 160 signatures.

Meanwhile the numbers for Republican and Democrat nominations remained close to what it's always been: 6,223 for the GOP and 5,801 for Democrats, both a small fraction of each party's voter registration.

Barry Hess, who has been the Libertarian candidate for governor every election since 2002, said the law is based on the flawed premise that members of his party — denied the chance to vote for one of their own — would instead mark the ballot for a Republican. He said without a Libertarian on the ballot they generally are more likely to protest by refusing to vote.

Or, Hess said, Libertarians could revolt.

“If we're not on the ballot, we're going to all vote Democrat,” he said.

GOP lawmakers who pushed the change made it clear they hoped to improve the odds for Republican lawmakers who might otherwise lose votes to a Libertarian.

“I can't believe we wouldn't see the benefit of this,” Rep. J.D. Mesnard said during a 2013 floor speech.

Since the law's passage, no minor party candidate running for statewide office has gathered enough signatures to be on the ballot in the primary.

That still left the possibility of minor party candidates qualifying for the ballot through write-in efforts during the primary. Hess pursued that path in his Libertarian gubernatorial bid this year.

But that same 2015 law required they get at least as many write-in votes as signatures they otherwise would have been required to get for regular nomination. And the formal election results announced this week found none of the three met that burden.

That clears the way for a head-to-head race between incumbent Republican Doug Ducey and Democrat challenger David Garcia, without either candidate having to worry about votes being siphoned off by Hess, though Angel Torres did qualify as Green Party candidate.

Hess said there is a need for a minimum signature requirement, but the number needed “should be low to accommodate an open field.”

“What they're trying to do is shut the field down completely, to win by exclusion,” he said.

Legal challenges by the Libertarians, however, have come up empty.

In a ruling last year, U.S. District Court Judge David Campbell acknowledged that the 2015 law sharply increased the number of signatures Libertarian candidates needed to qualify for ballot status. In some cases, the difference is more than 20 times the old requirement.

But Campbell said the new hurdle is not “unconstitutionally burdensome,” and accepted the arguments by state attorneys that the higher signature requirements ensure that candidates who reach the November ballot have some “threshold of support.”

The case now awaits a hearing at the federal appeals court.

Capitol Media Services contributed to this report.