MADISON, WI (WTAQ) - U.S. Senate candidate Tommy Thompson’s campaign reports the former Wisconsin governor sold stock he held in four companies because they have apparent ties to Iran.

The sale price was $38,000. A spokesperson for the campaign identified the companies at Royal Dutch Shell, Rio Tinto, a London-based mining company, Schlumberger, a Texas-based oil field service company, and Total Petroleum based in Africa.

The stock sale represents a small fraction of the Republican’s holdings.

Thompson is facing Madison Democratic Congresswoman Tammy Baldwin in the race for Wisconsin's open U.S. Senate seat.