As Arizona Gov. Jan Brewer prepared to make a career-defining decision — whether to veto a bill that would free business owners to discriminate on the basis of their religious preferences — a letter arrived at her office early this week with a stern warning from some of the biggest names in the local business community.

Signed by the heads of four Arizona business consortiums, with board members including officers of Bank of America, Intel and the Arizona Cardinals football franchise, the letter urged Brewer to strike down the measure known as S.B. 1062. The letter raised the prospect that the legislation could stain Arizona’s national reputation and touch off a wave of unpredictable litigation thanks to the bill’s broad, vague wording.

The Arizona legislation was an especially acute uproar over gay rights and religious liberty, but the larger dynamic at play there — pitting powerful business interests against ardent social conservatives — has played out over and over as the fight over same-sex marriage has spread across the country. In blue states like New York, big companies have played a pivotal role in pushing same-sex marriage measures into law. In battlegrounds like Virginia and now Arizona, corporate America has slowed or halted hard-right social policy from taking effect.

What Arizona proved, as much as any other in recent American politics, is that there’s currently no more powerful constituency for gay rights than the Fortune 500 list