Colorado, along with 25 other states, filed a lawsuit against the U.S. Postal Service to challenge a new rule that seeks to restrict the mailing of ballots to American citizens on an eligible voters list.

Colorado relies heavily on the mail-in ballot system. As do several states.

The U.S. Postal Service recently laid out how it would implement the order, but time is running short to impose major changes with some states beginning to send mail ballots to voters in just a few weeks.

A few days ago, the conservative majority of the Supreme Court had cleared the way for President Donald Trump’s executive order, which mandates the U.S. Department of Homeland Security to create those lists — to be given to states — and which bars the U.S. Postal Service from mailing ballots to people who are not on the lists of “enrolled” voters.

Colorado Secretary of State Jena Griswold said Colorado is still on track to mail ballots to voters as planned in October.

While the U.S. Supreme Court’s initial clearance of the order, it did not decide on the constitutionality of the new regulation— only on whether the challenge was premature when Democratic-controlled states persuaded a federal judge in Boston to suspend them in June. A second ruling from the same judge would prevent the Postal Service from implementing any procedural changes before this year’s midterms and would likely need to be nullified, as well.

In filing the lawsuit on Wednesday, the coalition of states argued that the Trump administration’s policies will prevent states from effectively administering their mail-voting programs, putting citizens’ right to vote at risk.

“This USPS rule is the latest attempt by the Trump administration to exert federal control over elections, cause mischief ahead of the midterm elections, and seize states’ constitutional authority to administer elections,” Colorado Attorney General Phil Weiser said in a statement. “States determine the time, place and manner of elections — not the president. And Congress has never given the USPS authority to regulate mail ballots. Most Coloradans vote using mail ballots.”

Trump, a critic of the mail-in voting system used in Colorado, has said it creates more opportunities for corruption and fraud. A main criticism from Trump has been that mail-in voting increases the possibility of unqualified voters, such as those living in the country illegally, to cast ballots.

Griswold often calls Colorado’s mail-in voting system the “gold standard,” stressing earlier this week that she was disappointed when the U.S. Supreme Court ruled in favor of allowing the Trump administration to move forward with policies outlined in an executive order penned in March.

There had been recent cases of noncitizens being registered to vote or voting. In New Jersey, about 6,600 noncitizens were registered, the result of a software glitch in that state’s automatic voter registration system. New Jersey Gov. Mikie Sherrill said about 400 of those noncitizens had cast ballots.

And in Colorado, Griswold, the state’s top election official, mistakenly sent 20,000 voter registration mailers to noncitizens in 2022.

In both Colorado and New Jersey, officials there said they would fight the rule or refuse to cooperate.

Additionally, Colorado’s mail-in voting system has encountered numerous problems, though the ballots affected were small and officials maintained the anomalies did not affect the outcome of elections.

• In 2019, Mesa County’s election office found some 500 ballots in a drop box — those ballots were never counted.

• In 2022, a commissioner race was omitted from the ballot for the Democratic primary in Pueblo County, compelling a reprint of about 70,000 ballots. Even after the reprint, some 1,600 ballots were sent still without the commissioner race. That same election year, a little over a dozen voters got ballots with the wrong state House race.

• Also in 2022, Denver’s election office uncovered that 60 voters got ballots for another precinct.

• In 2024, a dozen mail ballots were intercepted in Mesa County, filled out and turned in.

• Also in 2024, election officials in Denver and Adams counties investigated what they described as potential voter fraud after identifying “ballot irregularities” and mismatched signatures. The suspicious ballots came from the same daycare address.

Weiser’s office said the Trump administration’s rules inflict significant, irreparable harm on states by imposing burdensome mail-voting requirements that risk disenfranchising eligible voters.

With the start of the general election season mere weeks away, critics argued in the lawsuit that states must bear the cost of redesigning their mail ballot envelopes and securing USPS review and approval before they can even register mail voters with USPS.

They argued that, within a matter of weeks and without any additional resources, state election officials must also develop new systems to communicate mail voter lists to USPS to ensure that every person who is entitled to a mail ballot receives one. States must also create new guidance for election officials, train them on the new procedures and educate the public about the changes prior to the upcoming election, the lawsuit said.

In a statement Wednesday, Weiser’s office argued that even if states were to meet the administrative and financial burdens, the rule could still result in eligible voters not receiving their ballots due to, for instance, administrative errors or flaws in the rushed and untested new procedures.

The coalition further argued that the USPS rule violates the U.S. Constitution, which makes clear that states have the primary authority to administer elections, and upends successful, longstanding vote-by-mail procedures.

Joining Colorado in filing this lawsuit, which was co-led by the attorneys general of California, Massachusetts, Nevada and Washington, are the attorneys general of Arizona, Connecticut, Delaware, the District of Columbia, Hawaiʻi, Illinois, Maine, Maryland, Michigan, Minnesota, New Jersey, New Mexico, New York, North Carolina, Oregon, Rhode Island, Vermont, Virginia, Wisconsin, and the governor of the Commonwealth of Pennsylvania. 

Weiser’s latest filing brings his total to nearly 70 lawsuits against the Trump administration. A report from Center Square said the Attorney General’s Office has not provided information on how much those legal challenges have cost or which outside attorneys were hired to assist. After Weiser secured the Democratic nomination for governor, his office raised the fee to obtain those records from an initial estimate of $289 to more than $5,000, the Center Square said.

The Associated Press contributed to this report.