A letter to Republican voters advocating for Denver mayoral candidate Jamie Giellis failed to disclose that it was paid for by Giellis’ campaign.

The letter, dated April 11, went out to about 25,000 people. It was signed by several Republican activists and former officials under the name “Republicans for Jamie Giellis.”

The mailing didn’t include the usual “paid for” language required of political ads, though it was funded by campaign contributions. That was a mistake, according to campaign spokesperson Meghan Dougherty. There was no intent to deceive, she said: In fact, the envelopes listed the address for the campaign’s headquarters on South Broadway.

“Unfortunately, through an administrative error there was no disclaimer on the bottom of the final letter,” Dougherty wrote in an email. The letter’s signatories included a former state senator and a former chair of the local Republican Party.

Giellis has been registered as a Democrat or unaffiliated voter for her 13 years in Colorado, according to state records. The letter argued that she was the best choice for conservatives among a field of Democrats.

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“This race is too important to sit on the sidelines. We need a leader with the experience and vision who can take care of this city whether it’s filling potholes or stopping over-development in our neighborhoods,” the letter said. “This is not a Republican or Democrat issue, this is a quality of life issue that impacts us now and in the future.”

It recapped her campaign’s closing messages that she would end “runaway development” and “pay-to-play” practices, and said that Mayor Michael Hancock had “harassed” an employee when he sent sexually themed text messages in 2012. (He has denied that it was harassment.)

The letter also highlighted Giellis’ opposition to Initiative 300 — the campaign that’s trying to overturn the urban camping ban — and it tempered her approval of the pay-as-you-throw trash model, saying she won’t support new trash fees unless voters approve.

The campaign has about a month to settle the problem or otherwise respond, according to election officials, but it’s not clear yet how that will happen. The campaign responded with a letter Tuesday explaining the error, according to Dougherty.

The complaint was filed by a resident who received the letter. It was the first during this election against a mayoral candidate.