EDITOR’S NOTE: An earlier version of this story misstated the name of the chamber of commerce that received a donation from the Gill Foundation in 2015. It is the Indianapolis Chamber of Commerce.

The Texas Association of Business has been an outspoken opponent of the state’s proposed transgender bathroom bill, predicting the legislation will lead to a massive economic backlash and cost the state as much as $8.5 billion in lost business.

The Indianapolis Chamber of Commerce was similarly alarmed by the 2015 push for the Religious Freedom Restoration Act, arguing that it would negatively affect the state’s “ability to attract and retain jobs, talent and investment.”

Florida Competes, a small-businesses advocacy group in the Sunshine State, has tirelessly championed a bill that would make sexual orientation and gender identity protected classes under the Florida Civil Rights Act. The amendment, the group says, would boost Florida’s economic output by more than $5 billion and create nearly 36,000 jobs over the next 10 years.

These small-business coalitions and others across the country share a common source of funding: the national gay rights movement.

Since the legalization of same-sex marriage in all 50 states, the debate over gay and transgender rights has increasingly been framed in economic terms.

With prodding from the LGBT movement, powerful corporations have threatened to pull business out of states if their desired policy outcomes are not met.

Prominent gay rights organizations, including the Human Rights Campaign and the Gill Foundation, have also quietly poured hundreds of thousands of dollars into a network of small-business coalitions that routinely make doom-and-gloom economic prognostications about socially conservative legislation.

Tony McDonald, legal counsel of the conservative nonprofit Empower Texans, said the gay rights movement has relied more on corporate influence to implement its agenda since the legalization of same-sex marriage. Forcing Christian bakers to participate in same-sex weddings and allowing transgender people to use restrooms of the opposite biological sex just don’t carry the same emotional appeal as the fight for marriage equality.

“It was a multibillion-dollar effort to legalize gay marriage in the United States, and it’s not as if those people aren’t going to show up for work the next day,” Mr. McDonald said. “If anything, they’re going to try to be more active because they’ve won, and I think that’s what we’ve seen.”

Follow the money

Empower Texans published a leaked document on Aug. 1 showing that Keep Texas Open for Business, a coalition spearheaded by the Texas Association of Business, has received $130,000 in contributions from national gay rights organizations to oppose the state’s proposed transgender bathroom bill.

The two-page paper is titled “Coalition Investors” and shows $50,000 in donations from Gill Action, $15,000 from the Gill Foundation, $40,000 from the Human Rights Campaign and $25,000 from Freedom for All Americans.

That makes up nearly half of the $300,000 in total campaign contributions listed on the document. Other donors include Amazon, Apple and Intel.

The Texas Association of Business, which merged with the state chamber of commerce in 1995, said the document represents a snapshot of the movement’s donations at that time and is not representative of the coalition’s backers.

Texas Gov. Greg Abbott, a Republican, called a 30-day special session on July 18 to pass the bathroom bill and other legislative priorities.

The bathroom bill is opposed by House Speaker Joe Straus, a Republican, who says he is concerned that the bill would slow down economic growth and job creation.

In its campaign against the bathroom bill, the Texas Association of Business has commissioned multiplestudies predicting that the state could lose as much as $8.5 billion in gross domestic product and as many as 185,000 jobs.

One of the reports predicted that Texas would lose Super Bowl LI, which was played this year in Houston.

PolitiFact rated the prognostication “mostly false.”

Nonetheless, Mr. McDonald said the media routinely report those figures as fact in their coverage of the bathroom bill.

“We used to think TAB was just a rank-and-file, pro-business group,” Mr. McDonald said. “Not to say we agreed on everything, but that’s just kind of the way you view a chamber of commerce. But TAB doesn’t seem to be representing businesses in an even-handed, pro-business way. They’re not dealing in good faith.”

‘Punishing the wicked’

Tim Gill is the Colorado-based tech millionaire who has poured an estimated $422 million into the LGBT movement over the past two decades. In an interview with Rolling Stone published June 23, Mr. Gill said he wanted to “punish the wicked” in red states who disagree with his views on sexual morality.

The Texas Association of Business is one of Mr. Gill’s grantees.

Its 501(c)(3) arm, the Texas Association of Business & Chamber of Commerce Foundation, received $71,000 from the Gill Foundation in 2015, according to the Gill Foundation’s tax returns.

“The Gill Foundation is one of many contributors to the Texas Association of Business and Chamber of Commerce Foundation,” a spokesperson for the Texas Association of Business said.

The Texas Association of Business also received $25,000 from the Human Rights Campaign in 2014, according to the LGBT group’s annual report.

Texas state Rep. Matt Shaheen sent a letter to the Texas Association of Business Aug. 3 asking the group to disclose its ties to the LGBT movement.

“My question is, who are they representing?” Mr. Shaheen said. “They haven’t responded yet.”

He said the bathroom bill is “definitely not anti-business.” He pointed out that the legislation concerns only public facilities and gives private entities the option to regulate their restrooms however they choose.

“The bill is about what the proper role of government is,” Mr. Shaheen said. “The bill that the Texas Legislature is trying to pass says business should be able to manage their bathrooms however they want.”

A national effort

Similarly dire economic prognostications have followed socially conservative legislation in other states.

The Indianapolis Chamber of Commerce received $100,000 from the Gill Foundation in 2015. That year, it lobbied against the state’s Religious Freedom Restoration Act, a watered-down version of which was ultimately signed by then-Gov. Mike Pence.

At the time, chamber President Michael Huber said the bill would have a negative effect on Indiana’s “ability to attract and retain jobs, talent and investment” and would “encourage current and potential residents and visitors to take their business elsewhere.”

The Indianapolis Chamber of Commerce did not respond to a request for comment.

In 2014 and 2015, the Human Rights Campaign donated $165,000 to Competitive Arizona, $60,000 to Pennsylvania Competes and $25,000 to Florida Competes, formerly called Florida Businesses for a Competitive Workforce.

The Human Rights Campaign did not respond to a request for comment before press time.

Gregory T. Angelo, president of the Log Cabin Republicans, said he doesn’t see anything wrong with nominally pro-business coalitions taking up the cause for gay rights.

“Having an entity whose name does not explicitly address the issues at hand that are being championed by that entity is nothing new in Washington, D.C., in politics in general or in society,” Mr. Angelo said. “So I don’t see anything untoward about that.”

Zeb Pent, a spokesman for Stand for Fort Worth, said Silicon Valley should let the people of Texas govern themselves.

“If you know Texans, we don’t take kindly to blue state bullies and tech moguls who meddle in our affairs,” Mr. Pent said in a statement. “I think in light of Tim Gill’s published intentions, this is a telling revelation into how the national LGBT extremists are bullying their way into the reddest of states.”