The head of Apple, Tim Cook, has warned of "something very dangerous" happening in states across the US after Indiana passed a bill which it is feared will allow individuals and businesses to discriminate legally against homosexuals.

Cook, baptised in a Baptist church as a child and who now says he is "proud to be gay", said the bill rationalised injustice and went against the founding principles of the United States.

He was writing in The Washington Post after Indiana governor Mike Pence signed off the Religious Freedom Restoration Act that allows businesses to cite religious beliefs as a legal defence, such as when wishing to refuse a service to homosexuals.

Cook had already indicated his concern by tweeting earlier: 

In the Post, he went on to write: "These bills rationalise injustice by pretending to defend something many of us hold dear. They go against the very principles our nation was founded on, and they have the potential to undo decades of progress toward greater equality."

He added that similar legislation was being introduced in a "wave" in more than two dozen states and it will allow people to discriminate against their neighbours.

"America's business community recognised a long time ago that discrimination, in all its forms, is bad for business. At Apple, we are in business to empower and enrich our customers' lives. We strive to do business in a way that is just and fair. That's why, on behalf of Apple, I'm standing up to oppose this new wave of legislation — wherever it emerges. I'm writing in the hopes that many more will join this movement. From North Carolina to Nevada, these bills under consideration truly will hurt jobs, growth and the economic vibrancy of parts of the country where a 21st-century economy was once welcomed with open arms."

He said faith has always been an important part of his life but he was never taught, nor does he believe, that religion should be used as an excuse to discriminate.

"Men and women have fought and died fighting to protect our country's founding principles of freedom and equality. We owe it to them, to each other and to our future to continue to fight with our words and our actions to make sure we protect those ideals. The days of segregation and discrimination marked by "Whites Only" signs on shop doors, water fountains and restrooms must remain deep in our past. We must never return to any semblance of that time. America must be a land of opportunity for everyone."

The new law has prompted protests across the nation. Dan Malloy, governor of Connecticut, today signed an executive order banning state-funded travel to Indiana

San Francisco and Seattle have imposed similar bans. Angie's List has pulled out of a campus expansion project in Indianapolis and the Salesforce software corporation has warned it will "dramatically reduce" its investment in Indiana.