PHOENIX — A voter advocacy group, a union and Democratic lawmakers are asking a judge to void a new Arizona law expanding the ability of some groups to make anonymous “dark money” contributions to political campaigns.

The lawsuit filed Wednesday in Maricopa County Superior Court contends the Republican-controlled Legislature acted illegally earlier this year in exempting some organizations from laws requiring them to register before they can spend money to influence elections. That means they may avoid disclosing to voters who provided the cash in the first place.

Attorney Jim Barton filed suit for the Arizona Advocacy Network, the Brickworkers and Allied Crafterworkers Union Local 3 and more than two dozen Democratic lawmakers. He said there are other legal flaws in the law.

One, he said, is that the exemption lawmakers provided to certain nonprofit organizations applies only to those also registered with the Arizona Corporation Commission. But Barton said the legislation denies the same privilege to unions which, while organized as nonprofits, do not register with the commission.

Potentially the most sweeping contention is that lawmakers violated a constitutional provision requiring the Legislature to have laws to tell the public about all contributions to, and expenditures of, campaign committees and candidates for public office.

Barton said the new state law, known as SB 1516, allows nonprofits and similar entities to make unlimited contributions to political parties. Then the parties can spend unlimited amounts of money on behalf of their nominees.

“Since the reporting of these particular contributions are not required, then built-in disclosure safeguards (required by the Arizona Constitution) are broken,” Barton wrote.

A spokesman for the Secretary of State’s Office, which enforces the campaign finance laws, said the lawsuit is being studied.

The new law, pushed through largely along party-line votes, was a major overhaul of campaign finance laws.

It allows individuals to spend unlimited amounts of money to help raise funds for candidates they support without having to disclose it to the public.

Another provision scraps the $100 cap on what people can spend on tickets, food and liquor for fundraisers for candidates without having to disclose the source of those dollars.

Most significant, it eliminates laws that require groups spending money to influence elections to register first with the state. These same groups also can refuse to disclose donors to the public if they are registered with the Internal Revenue Service as a “social welfare” organization.

The law’s prime architect was Rep. J.D. Mesnard, R-Chandler, who is now speaker of the Arizona House.

“I think transparency is a good principle,” he said during debate at the time. “But it is not the overarching principle.”

He cited a 1950s case in which the U.S. Supreme Court ruled that the state of Alabama could not force the NAACP to disclose its members in order to do business in the state because it could lead to harassment of those members. Mesnard said donors to “dark money” groups are entitled to the same protection, suggesting the government could go after those whose views it does not like.

“We have a right to speech, which our money is speech,” Mesnard said. “We have a right to privacy in those associations.”