The international food giant, General Mills, has publicly declared it opposes a proposed constitutional amendment to ban equal marriage in Minnesota, and has consequently angered anti-equality groups in the state.

The Fortune-500 company is based in Minnesota, where, at a ballot measure this November voters will decide whether to ban equal marriage in the state. The Obama administration opposes the measure.

At a meeting for gay and lesbian professionals in the company this week, CEO Ken Powell affirmed his opposition for the proposed amendment, which the company’s vice president for global diversity and inclusion, Ken Charles, formally endorsed in a letter.

“We do not believe the proposed constitutional amendment is in the best interests of our employees or our state economy,” Mr Charles wrote in an e-mail. “We value diversity. We value inclusion.”

General Mills, the name behind many of world’s popular cereal brands, is the first major international organisation in the state to openly declare their opposition to anti-equality legislation, though they were preceded in this at the local level by St Jude Medical, which manufactures devices for health industry.

The anti-equality group, National Organisation for Marriage (NOM), which runs campaigns against marriage equality around the US, has been quick to condemn the food giant for declaring ‘war on marriage.’ The group, which currently boycotts Starbucks for their pro-equality stance, has also sent letters to 50 of the state’s largest companies, urging them to remain neutral on the measure.

Richard Carlbom, campaign manager for an anti-amendment group, praised the decision of the company, saying: “The business case against this amendment is straightforward and powerful.”

Media commentators note that this was a sign that companies around the US are becoming bolder in their support for gay rights and marriage equality. Recently, 50 major companies, including Nike, Xerox and Time Warner, signed a court briefing against the Defense of Marriage Act (DOMA), which denies federal benefits to same-sex couples.