Big business has ratcheted up its objections to proposals that would make it harder to vote, with several hundred companies and executives signing a new statement opposing "any discriminatory legislation."

The letter, published Wednesday in The New York Times and The Washington Post, was signed by companies including Amazon, Google, Starbucks and Bank of America, and individuals such as Warren Buffett and Michael Bloomberg, plus law firms and nonprofit groups.

It was the largest group yet to join protests against Republican efforts to change election rules in states around the country.

"Voting...