By Daniel Bice | Milwaukee Journal Sentinel

Republican U.S. Senate candidate Tommy Thompson sold his stake earlier this year in yet another company that had done business in Iran, his campaign said this week.

Lisa Boothe, spokeswoman for Thompson, said the former four-term governor dumped his ownership interest in the state-controlled China Petroleum and Chemical Corp., or Sinopec, in January.

In his personal financial disclosure form filed on Jan. 27, Thompson said he owned up to $1,000 of Sinopec stock

"The Governor's financial adviser sold the stock that was mentioned in this article in 2012 as a result of an investment strategy," Boothe said. "Just as the Governor promised, he has rid himself of any stocks that have any business dealings with Iran, no matter how minor."

A 2010 U.S. Government Accountability Office report listed Sinopec as one of 41 foreign firms engaged in commercial activity in Iran's oil, gas or petrochemical sectors. The Wall Street Journal reported in 2006 that Sinopec had an agreement with Iran to develop an oil field in the country's southwestern region.

Last week, Thompson sold stock in four companies for about $38,000 after The Huffington Post reported that the firms had ties to Iran. Thompson also disclosed that he dumped his holdings in two other companies with ties to Iran about 10 months ago.

Thompson has been very critical of his opponent, Democratic U.S. Rep. Tammy Baldwin, for voting against Iranian sanctions four times and taking nearly $60,000 in donations from a group opposed to sanctions. He has also said the U.S. should consider cracking down on Russia and China for backing Iran's nuclear efforts.

But a Baldwin staffer said the disclosure that Thompson invested in yet another foreign company that has done business in Iran raises troubling questions.

"There are seven interests tied to Iran," said Baldwin spokesman John Kraus. "What did he know and when did he know it? And when did he rid himself of these seven interests?"