S EATTLE — Conservatives here, a droll minority, say that under this city’s quota system, when a conservative enters the city, one already here is required to leave. They also say Washington is actually two states:

There is what you can see from atop this city’s Space Needle — mea

ning, this liberal city — and there is everything else, extending to the Oregon, Idaho and Canadian borders.

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 Supreme Court has held that disclosure requirements serve three government interests: They provide information about the flow of political money, they deter corruption and avoid the appearance thereof by revealing large contributions, and they facilitate enforcement of contribution limits. These pertain only to financial information in candidate elections. These cannot justify compelled disclosures regarding referendums because referendums raise no issues of officials’ future performance in office — being corruptly responsive to financial contributors. The only relevant information about referendums is in the text of the propositions.

In 1973, Washington’s secretary of state ruled that signing an initiative or referendum petition is “a form of voting” and violating voters’ privacy could have adverse “political ramifications” for those signing. In 2009, some advocates of disclosure plan to put signers’ names on the Internet in order to force “uncomfortable” conversations.

Larry Stickney, a social conservative and president of the Washington Values Alliance, says disclosure of the identities of petition-signers will enable “ideological background checks” that will have a chilling effect on political participation. He frequently encounters people who flinch from involvement with the referendum when they learn that disclosure of their involvement is possible. He has received abusive e-mails and late-night telephone calls, and has seen a stranger on his front lawn taking pictures of his house.

The Wall Street Journal’s John Fund reports that some Californians who gave financial support to last year’s successful campaign for Proposition — it declared marriage to be only between a man and a woman — subsequently suffered significant harm. For example, the director of the Los Angeles Film Festival, who contributed $1,500, was forced to resign. So was the manager of a fashionable Los Angeles restaurant who contributed just $100.

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. He let us down, too, remember, and many of you still gave him a job.”

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.

And when Humana, the private health insurance provider, recently warned its customers about some provisions of Congress’ health care legislation, the Obama administration’s reaction was essentially a quote from a Ring Lardner short story: “Shut up, he explained.”

It is time to speak up about thuggish liberalism, especially when it tries to suppress participation in referendums, which often involve contentious issues. 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.

George Will is a Washington Post columnist. His e-mail address is georgewill@washpost.com.