Voters are going to get the final say on whether Colorado should give all nine of the state’s Electoral College votes to the winner of the national popular vote for president.

The Colorado Secretary of State’s Office certified Thursday that opponents of the state joining the national popular vote compact collected enough valid signatures to put the issue on the ballot in November 2020.

“We’ve had so much support and grassroots volunteers, so this is a real victory for us,” said Rose Pugliese, a Mesa County commissioner and organizer behind the petition drive.

And it’s unusual. The last time a challenge of a law went on the ballot was in 1932, after the legislature passed a tax on Oleo margarine. According to the Secretary of State’s Office, the tax was overturned by Colorado voters.

Pugliese and Monument Mayor Don Wilson started a group this past spring in the hopes of doing the same thing to a bill passed by Democrats during the 2019 state legislative session to join the compact.

The compact says each state promises to give its Electoral College votes to the winner of the national popular vote for president no matter who won in each state. Fifteen states and the District of Columbia have joined the compact for a total of 196 electoral votes. That’s fewer than the 270 votes needed to elect a president, and the compact — as well as the law in Colorado — won’t go into effect until it clears that threshold.

The way the Electoral College works is every state gets one electoral vote for each of its U.S. representatives and senators. A sparsely populated state such as North Dakota has three electors, while Colorado has nine — even though North Dakota has one-fifth the population of the Centennial State. Supporters say this ensures smaller, more rural states still get a say in who becomes president.

U.S. Rep. Ken Buck, chairman of the Colorado Republican Party, hailed the success of the petition effort Thursday.

“Today, grassroots Coloradans sent a clear message to overreaching Democrats at the state Capitol,” he said in a statement. “Colorado’s presidential choice should be controlled by Colorado voters, not population centers in New York and California.”

Supporters of the law are organizing, too. They already have formed their own issue committee, Yes on National Popular Vote. Their argument for scrapping the current system: One vote shouldn’t count more than another just because someone lives in a different state. It’s the fairest way to vote, and it’s how we elect people to every other federal office.

“Our focus today is simple — to build the political organization required to win this campaign and bring our country on important step closer to having a popular vote for president,” said Patrick Rosenstiel, who runs the Yes campaign.

The debate over the national popular vote likely will find its way into the 2020 race for U.S. Senate. Incumbent Sen. Cory Gardner has been an outspoken critic of the compact and donated $50,000 to Colorado’s repeal effort through his committee, Project West PAC. Most of the Democrats hoping to challenge Gardner haven’t publicly weighed in on the issue yet, but one — former state Sen. Mike Johnston — has said he supports reforming the Electoral College.

Another wrinkle in the debate over the Electoral College is a decision this month from a federal appeals court. The 10th U.S. Circuit Court of Appeals ruled that three presidential electors from Colorado were unconstitutionally forced to cast their votes for Hillary Clinton in 2016.

“I think that this decision only highlights the need to abolish the archaic Electoral College,” Gov. Jared Polis told reporters at a recent news conference. “I mean, if voters in our state vote for somebody, and we can’t even make sure that’s who our electors vote for, it’s clearly time to not have this archaic, undemocratic institution of electors and move to direct popular vote for president.”