HELENA — Gov. Steve Bullock revived debate over mail-only voting on Friday when he used his veto power to rewrite a routine bill to allow counties to conduct the May 25 congressional election by mail.

The governor’s action caught Secretary of State Corey Stapleton off guard. His fellow Republicans in the House, who had killed the bill last month, were scrambling to see if there was a way to prevent the governor’s changes from being debated and getting a floor vote. They might be able to run down the clock — because they can choose to take up the matter any time during the remaining days of the session.

The 11th-hour political maneuver might be too late for some counties, who are already planning to print ballots, arrange polling sites and assemble thousands of poll workers.

Fewer than seven weeks remain before the special election to fill the state’s only congressional seat, which was left vacant when Ryan Zinke resigned to lead the U.S. Interior Department. Republican Greg Gianforte, Democrat Rob Quist and Libertarian Mark Wicks are contesting for the post.

“At this point, many of us clerks can’t keep fighting the battle in Helena. Our focus has to be on the election at hand,” said Regina Plettenberg, the chief elections officer for Ravalli County. “At this point, we are planning on running this election at the polls.”

Using his veto pen, Bullock rewrote an election bill awaiting his signature. The original bill, sponsored by Democratic Rep. Bryce Bennett of Missoula, mostly addressed mundane election rules such as noticing requirements, clarifying deadlines for local elections.

“I take seriously my responsibility to strengthen our democracy by helping make sure that more eligible citizens can participate in that democracy, not fewer,” the governor said in a press conference announcing his action. “And what is better for democracy than to put a ballot in the hands of every registered voter?”

The governor’s amendatory veto inserted an entirely new section into Bennett’s 22-page bill, specifying that “the 2017 special election to fill the vacancy in the office of the United States representative for Montana may be conducted by mail.”

The governor is allowed by state law to issue so-called “amendatory vetoes” to bills he generally supports but will only sign with his suggested changes.

The issue became a partisan one when the chair of the state’s Republican party, Rep. Jeff Essmann, warned earlier this year that conducting voting by mail could make it easier for Democratic voters to cast ballots and hurt his party’s chance of holding a congressional seat occupied by Republicans for two decades.

House Republicans shot back at the governor saying that mail-only balloting is bad policy.

“It’s unfortunate that he’s trying to use his power to shoehorn a completely different piece of legislation into a simple cleanup bill that has already moved through the process,” said Lindsey Singer, the spokeswoman for the leadership of the Republican-controlled House.

The Senate had already consented to the mail-only ballot, but House Republicans successfully blocked the measure from a floor debate. Most thought the effort had died last week when the House rejected a bid to revive the bill sponsored by Sen. Steve Fitzpatrick, a Republican from Great Falls.

Country elections officials have been pushing lawmakers to allow the election to be conducted by mail, arguing that it could save them as much as $750,000, as well as save them from the logistical nightmares of running an election on short notice.

County clerks face a Monday deadline to present their election plans to the Secretary of State’s Office, but it’s unclear what kind of leeway exists in state election laws that would allow them to pursue a mail-only election beyond the current schedules already outlined. A spokeswoman for the secretary of state did not immediately respond to requests for comment.

While some counties have little choice but to move forward with in-person voting, some could quickly shift gears, according to Plettenberg, the Ravalli County clerk.

“If by next week, by some miracle in Helena things get switched to a mail ballot,” she said, “then I can easily switch.”