Legislation that would require disclosure of donors to groups that support political candidates and causes passed the state Senate Elections Committee Tuesday.

Senate Bill 1403 would require groups to reveal names of their donors in what is characterized as a way to shed light on "dark money" in politics.

The bill passed unanimously and has bipartisan support. But it has detractors, including lawmakers and representatives of political groups who say that forcing groups to reveal donors will keep some people from donating.

"When we're talking about these First Amendment rights, we also need to be aware of the fact that disclosure of some of these speakers may result in a chilling effect, and this chilling effect could suppress speech," Michael Liburdi, a lawyer with the Arizona Victory Alliance, told committee members.

Under questioning from lawmakers, Liburdi declined to reveal activities of the alliance and whether it would be involved in the current election cycle. He cited the attorney-client privilege, saying only that the alliance is a nonprofit.

The Arizona Daily Star reported Wednesday that the alliance spent more than $475,000 in the last election cycle to elect Republicans and defeat Democrats.