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Now it's Willis Tower.

Today's the switch, with the 110-story Chicago skyscraper known as the Sears Tower now officially called the Willis Tower.

The Chicago Tribune says the letters on the building were changed Wednesday.

But as CNN.com points out, more than 90,000 people have signed up on Facebook with a group called People Against the Sears Tower Name Change.

"That's not gunna fly," the organization writes. "This group is for Chicagoans and whoever else against the name change. It's for the people who will always call the tallest building in the u.s. THE SEARS TOWER."

If you agree, there's an online petition here.

Update at 11:30 a.m. ET:

Chicago Public Radio reported today about the tower's $350 million "green makeover."