Donors may regret writing that year-end check to their favorite Colorado nonprofit, particularly if there’s a chance that nonprofit will have something to say about proposed laws in the city of Denver.

Under a recently enacted Denver ordinance, nonprofits that spend more than $500 communicating with voters about a ballot question must give the city the names and addresses of anyone giving more than $50. For donors giving more than $200, the city also wants to know donors’ occupations and the names of their employers.

Denver is not alone. Laws like this are spreading across the country. From Denver, to Santa Fe, New Mexico, to Tempe, Arizona, cities are demanding donor lists from nonprofits that communicate with voters about issues on the ballot. But these laws don’t just invade people’s privacy and threaten the speech of nonprofit groups – they’re also unconstitutional.

Everyone has the right to support causes they believe in – and to do so privately – under the First Amendment to the U.S. Constitution and the free-speech clause of the Colorado Constitution. That is why two Colorado nonprofit groups, the Colorado Union of Taxpayers Foundation and the TABOR Committee, have joined with the Goldwater Institute to challenge the city of Denver over its new law. They are asking a state court to declare Denver’s law unconstitutional in order to protect the rights of free speech, association, and privacy of Colorado nonprofits and their donors.

As the U.S. Supreme Court recognized nearly 60 years ago, in NAACP v. Alabama, when the government obtains and publicizes a group’s list of donors, those supporters are immediately placed at risk of harassment and intimidation by their ideological opponents. This continues to be true today, with the internet making it simple to find and harass perfect strangers simply because they hold a different point of view. The government may not be the one harassing people, but it enables private individuals to harass others by publicizing lists of donors to various causes.

Donors understand this, and as such, they are significantly less likely to give to a nonprofit if they know their privacy might be threatened. That is why protecting donor privacy is seen as a cardinal virtue among nonprofits nationwide.

Denver will say, as the government always does, that it doesn’t want anyone to get harassed – it simply believes people have a right to know who is giving to these groups. But whether that is true or not, courts have repeatedly said that this inchoate “informational interest” is minimal relative to the concrete free speech and associational interests of nonprofits and their donors. Many nonprofits have donor lists that are thousands of individuals long. The government should not be in the business of making these people’s names, addresses, occupations, and employers available to their ideological opponents.

The end result of Denver’s law will not be more lists of donors made public. Nonprofits are too protective of their supporters to let that happen. Instead, most nonprofits will simply choose to remain silent, thereby depriving the public of important messages and relevant information the next time there is a question on the ballot. Fewer voices and less information will not strengthen our democracy, nor allow voters to make better decisions. Nonprofits have an important voice in the public debate. Denver should let them speak.