A coalition of more than 400 companies is openly opposing a Georgia “religious liberty” bill that is rapidly heading toward passage, with at least one major company already leaving the state over the proposal.

The proposed law would allow both individuals and organizations to refuse to conduct business with or otherwise discriminate against anyone whose marriage they find counters their religious beliefs. It also protects individuals from existing nondiscrimination laws in Atlanta and elsewhere.

A similar bill was dismissed last year, but the speed at which this year’s version, the “First Amendment Defense Act” (FADA), is moving has raised serious concerns among state lawmakers, business owners, the faith community and activists.

The bill passed both the House and, in a different form, the Senate this month. The most recent version bars the government from taking “adverse action” against a person or faith-based organization that “believes, speaks, or acts in accordance” with the religious belief that “marriage should only be between a man and a woman”.

Telecom startup 373k announced it would to relocate from Decatur, Georgia, to Nevada immediately after the Georgia senate voted in favor of the measure last week.

“I don’t want to be in a state where it is hard to attract the best talent,” said founder Kelvin Williams, who is gay.

Mary Moore, a local business owner, said: “I think there’s been a lot of strong opposition to [FADA] ... I think the voices are a lot louder because everybody is now concerned that it’s actually going to pass.”

Based on the over 500 emails he’s received from members of his district and elsewhere, House Representative Taylor Bennett agrees there’s “overwhelming opposition” to the proposed law.

Just in the last week, roughly 100 businesses have joined a coalition of what is now over 400 companies opposing the religious freedom bill. The group Georgia Prospers, of which Moore is a member, includes a range of businesses – from Fortune 500 companies like Delta, Coca-Cola, and Home Depot to smaller ones across the state – in support of “treating all Georgians and visitors fairly”.

Several have cited fears that Georgia will suffer lost revenue, as in Indiana where public disdain for a similar bill, before it even became law, is said to have cost the state $60m. Atlanta’s chamber of commerce and visitors’ bureau produced separate studies citing a potential loss of $1bn to $2bn if the bill passes without civil rights protections.

The religious community is also represented among the many in opposition to the law. Nearly 300 clergy members in the state spoke out this week against the “overly broad, discriminatory” proposal.

“The title speaks for itself,” said representative Stacey Abrams, Georgia’s House minority leader. “There is a question about whether the first amendment needs to be defended – it does not. Nothing that has happened in state or federal law has unsettled the constitutionality of the first amendment.”

Joe Whitley, former US attorney and Department of Justice official, calls the proposed law “superfluous and unnecessary” in a legal analysis. “The first amendment in and of itself protects all Americans’ rights to speech, to worship freely, and to be free from a state-established creed,” he said. “These rights do not need the General Assembly to legislate in order to give them force or effect.”

Not only does the bill allow individuals and faith-based organizations to discriminate against same-sex couples, but also against anyone perceived to have sexual relations outside of a heterosexual marriage, such as single parents, or unmarried couples, whether gay or straight.

A number of “easily foreseeable” scenarios that could arise if the law were to pass are included in Whitley’s analysis: a restaurant refusing service to an interracial couple; a hospital denying a man the right to visit his male spouse; a business refusing to hire a single woman living with her partner. The same kind of discrimination on the part of an employer, landlord, or public employee could be protected under FADA.

Supporters argue the law is needed to protect the religious freedom of individuals to exercise their “sincerely held” religious beliefs as they pertain to marriage.\

State senator Greg Kirk, who proposed an earlier version of the bill in the Senate, argues that faith-based organizations risk being discriminated against by the state for acting in accordance with their religious beliefs. He points to the Catholic Church’s policy of permitting adoptions only to to male-female couples and not same-sex.

“Knowing the history of the State of Georgia, I don’t see that as an issue,” said Abrams. “But I do see this bill being used to preclude and forbid same-sex couples from adopting – and that should be the worry that we have … the reality of what has happened in several states in this nation.”

State Senator Nan Orrock remembers the “battles that raged across the South” after US supreme court findings established a law that people of color are equal. “The southern states did the same sort of thing back then,” she says, referring to attempts by state governments to circumvent federal protections using Jim Crow laws. “It all boils down to sanctioned discrimination.”

“I don’t believe it’s ever been about party lines,” said Abrams. “Discrimination is not a partisan issue.” She expects both Republicans and Democrats in the House to stop the bill from passing, “when people really understand what this bill proposed by the Senate will do”.

“And the House, I doubt, will stand for it.”