SEATTLE — On Tuesday, Washington residents will vote in a referendum that has national significance because of a controversy about disclosing the names and addresses of those who signed petitions to trigger the referendum. Disclosure threatens the right to privacy, which is under assault by a spreading movement — call it thuggish liberalism — that uses intimidation to suppress political participation.

The referendum is on a new state law that some say establishes same-sex marriage. This is a matter about which people differ. What is, however, unambiguously wrong is the attempt by some supporters of the law to force disclosure of the names and addresses of the 138,000 people who signed the petition bringing about the referendum. This can have no other purpose than to make it possible to harass those signers.

Those favoring disclosure say it is mandatory under the state’s Public Records Act. If so, that act is unconstitutional. In the 1950s, Alabama tried to compel the NAACP to disclose its membership list. The U.S. Supreme Court ruled that disclosure would burden the freedoms of expression and association that the First Amendment protects.

Advocates of compelled disclosure predictably invoke Louis Brandeis’ axiom that sunlight is the best disinfectant. But what is the supposed infection?

The Wall Street Journal’s John Fund reports that some Californians who gave financial support to last year’s successful campaign for Proposition 8 — it declared marriage to be only between a man and a woman — subsequently suffered significant harm. The manager of a fashionable Los Angeles restaurant who contributed just $100 was forced to resign.

Charles Bouley, a gay columnist, has honorably protested such bullying. He says people “have the right to be wrong” and reminds gay activists: “Even Barack Obama said marriage was between a man and a woman at a time when we needed his voice on our side on equality.” Obama’s home phone number (202-456-1414) and address are known, but it is hard to harass someone surrounded by Secret Service protection. Less-insulated Americans are vulnerable. Currently, liberals enthralled by intimidation are trying to abolish secret ballots in unionization votes.

It is time to speak up about thuggish liberalism, especially when it tries to suppress participation in referendums. The Supreme Court has blocked disclosure of the 138,000 names. It should block the spreading infection of using disclosure as a tool of liberal coercion.