PNM, which provides electricity in New Mexico, has also quit the Chamber.

Nike stopped short of quitting the Chamber, but it has resigned its seat on the Chamber's board.

Some 25 large companies—including DuPont, BP America, Ford Motor Company, and General Motors—have joined the United States Climate Action Partnership, a group focused on supporting cap-and-trade legislation.

But the resignations don’t mean the Chamber is entirely out of step with the nation’s business community. There are plenty of businesses that view climate-change regulation or legislation very skeptically.

And they aren’t insignificant businesses either.

Valero Energy, which ranks 10th on the Fortune 1000 list of largest U.S. companies, recently launched a website opposing the legislation. It fears the legislation could ruin its oil-refining business.

Valero would have to buy credits for the 327 million metric tons of CO₂ the company emits. The current price of such credits on the European market, where carbon emissions have been regulated for several years, would be between $6 billion and $7 billion.

“The best year we ever had was in 2005, when we had $5 billion in profits on $110 billion of revenue,” Jim Greenwood, vice president of government affairs, tells the San Antonio Business Journal. “Granted that we bring in a lot of revenue on gas sales, but our margins are razor thin.”

On Monday, as Apple quit the Chamber, the governor of Texas vowed to fight greenhouse-gas regulation as he took on his new role as chairman of the Interstate Oil and Gas Compact Commission—the oil-and-gas-producing states’ lobbying voice in Washington since 1935.

Governor Rick Perry said the legislation would cripple his state’s energy sector, the Dallas Business Journal reports.

“More mandates, restrictions, and penalties are not the kind of thing that will encourage innovation and investment. As it stands, this bill would usher in the single-largest tax in the history of our nation, along with an unprecedented degree of federal intrusion into every American farm, home, and workplace,” Perry said. “These energy taxes will cause every product that uses energy in its creation, cultivation, or transportation to become more expensive, forcing hardworking Americans to bear massive new costs and kicking the legs out from underneath a national economy that is already wobbling.”