The celebrity Web site TMZ.com posted two photographs Tuesday showing Shriver holding a phone to her ear while she's behind the wheel. It says one was snapped Sunday and the other in July.
On his Twitter feed Tuesday, Schwarzenegger wrote to TMZ.com founder Harvey Levin: "Thanks for bringing her violations to my attention. There's going to be swift action."
Schwarzenegger spokesman Aaron McLear says that by "swift action," the governor means he'll ask his wife not to hold the phone while driving. A law that took effect in 2008 requires California drivers to use a handsfree device.
The first lady's office said it would have no comment.