Rev. Ken Hutcherson, pastor of Antioch Bible Church in the east Seattle suburb of Redmond - also home to Microsoft - said he would officially make the call for the boycott Thursday on a national conservative talk radio show, Focus on the Family.
"We're tired of sitting around thinking that morals can be ignored in our country," he said. "This is not a threat, this is a promise. Check out the past presidential election. We made the moral issue the No. 1 issue."
Last week, several companies, including Microsoft Corp., Boeing Co., Hewlett Packard Co., and Nike Inc. signed a letter urging passage of the measure, which would add "sexual orientation" to a state law that already bans discrimination in housing, employment and insurance based on race, gender, age, disability, religion, marital status and other factors.
Microsoft's support comes a year after it was denounced for quietly dropping support for it.
Hutcherson, who has organized anti-gay-marriage rallies in Seattle and Washington, D.C., was at the middle of the Microsoft controversy last year on the gay rights issue. He says he pressured Microsoft into dropping its support of the measure last year by threatening a boycott.
The company, which took heat from gay activists across the country, insisted it decided to take a neutral stance to focus on other issues but later came out saying it would once again support the measure in future years.
Asked about Hutcherson's threat Monday, Microsoft spokesman Lou Gellos said, "Our position is well known, as we said in our letter last week, and we stick by it." He declined to comment further.
Boeing spokesman Peter Conte said the company had no plans to withdraw its support.
"The position that we have taken is one that we do feel strongly about," he said. "It is entirely consistent with our own internal practices and policies."
Other companies did not return phone calls on Monday, the Martin Luther King Jr. holiday.
Rep. Ed Murray, D-Seattle, who has sponsored the measure for more than a decade, said he wasn't concerned that Hutcherson's move would have any impact on the companies' bottom line.
"The American people and citizens of Washington state aren't going to buy into his line of bigotry," he said.
Hutcherson said he has the support of several national organizations, including the Family Research Council, Southern Baptist Convention and Focus on the Family. Several of those organizations' offices could not be reached after hours Monday.
Dr. Joseph Fuiten, a Bothell pastor who is chairman of Faith & Freedom Network, an organization that opposes the bill, said the boycott is a signal "that we're out here too."
Fuiten said that Christian consumers "don't like to see companies use their financial muscle to promote what we view as immoral."
"These companies should stick to their business, make their widgets," he said. "Why are they trying to engineer social policy for America?"
Hutcherson said he's not telling companies to change their own internal policies on gay rights. He just doesn't want them influencing lawmakers with their support.
"Don't step in our world, we won't step in yours," he said.
Supporters of the bill said that that the groups don't represent the state's citizens.
"It's sad that on the day we remember Martin Luther King Jr., that a small minority of people believe it's OK to fire someone or deny them housing simply because they're gay," said Fran Dunaway, executive director of Equal Rights Washington, a group formed to support the gay civil rights bill.
The bill has been introduced - and rejected - annually for nearly 30 years in the Legislature.
The state House last year passed the bill 61-37, with six Republicans joining 55 Democrats in favor. But it lost by one vote in the Senate, where two Democrats, Jim Hargrove of Hoquiam and Tim Sheldon of Potlatch, joined 23 Republicans in defeating the bill.
The measure is believed to have a better chance of passage this year because Sen. Bill Finkbeiner, R-Kirkland, announced last week that he would switch his vote to yes.
A House committee planned a public hearing on the bill on Tuesday.
The gay civil rights bill is House Bill 2661.