SPRINGFIELD -- The chairman and CEO of Peoria-based Caterpillar Inc. is raising the specter of moving the heavy equipment maker out of Illinois.

In a letter sent March 21 to Gov. Pat Quinn, Caterpillar chief executive officer Doug Oberhelman said officials in at least four other states have approached the company about relocating since Illinois raised its income tax in January.

"I want to stay here. But as the leader of this business, I have to do what's right for Caterpillar when making decisions about where to invest," Oberhelman wrote in the letter obtained Friday by the Lee Enterprises Springfield bureau. "The direction that this state is headed in is not favorable to business and I'd like to work with you to change that."

Oberhelman said he's being actively courted to move.

"I have been called, 'cornered' in meetings and 'wined and dined' -- the heat is on," Oberhelman wrote. "Before, I never really considered living anywhere else and certainly never considered the possibility of Caterpillar relocating. But I have to admit, the policymakers in Springfield seem to make it harder by the day."