Democrats who have been hammering away at Halliburton Co. and its former chief executive Dick Cheney about the company's work in Iraq yesterday added Iran to their list of complaints.

In a conference call with reporters, Sen. Frank Lautenberg (D-N.J.) said he found it "unconscionable" that a Halliburton subsidiary appeared to be doing business with a country tied to terrorist activities at a time Cheney was Halliburton's chief executive.

The conference call, organized by the presidential campaign of Sen. John F. Kerry (D-Mass.), came one day after Halliburton disclosed that a federal prosecutor had subpoenaed documents as part of an investigation of whether a Halliburton subsidiary violated anti-terror sanctions on Iran. "This is such an outrageous bit of news," Lautenberg said.

In a filing with federal regulators Monday, Halliburton disclosed that the three-year investigation had escalated from an inquiry by the Treasury Department's Office of Foreign Assets Control to a criminal investigation by the Justice Department.

Such cases are referred to Justice only when there is evidence "intentional or willful" violations have occurred, government officials said.

The Justice Department investigation relates to a subsidiary called Halliburton Products & Services Ltd., an oil field services company incorporated in the Cayman Islands. In a 2003 report, the company said the subsidiary "performs between $30 [million] and $40 million annually in oilfield service work in Iran."

According to financial disclosures filed with federal regulators, the company received an inquiry in 2001 about possible violations of national security sanctions that prohibit U.S. companies from doing business in Iran. Under federal sanctions law, foreign subsidiaries of U.S. companies can do business in a sanctioned country only if its operates independently of the parent company.

Halliburton has said repeatedly in documents on file with the government that its subsidiary operated legally in Iran, outside the control of U.S. executives.

"We look forward to answering any and all questions. It is important to understand, especially in the current political environment, that this is not a condemnation of the company, but a method of further studying the facts," Halliburton spokeswoman Wendy Hall said in an e-mail yesterday, referring to the Iran subpoena. "We welcome a thorough review of any and all of the company's business. We continue to believe that Halliburton's business in Iran is in compliance with applicable laws and regulations."

Cheney's office referred calls to the Bush campaign, which played down the disclosure. "This was the daily baseless political attack by the Democrats," said Bush campaign spokesman Steve Schmidt. "Today the hatchet man was Frank Lautenberg. . . . This is an attempt by the Kerry campaign to avoid a discussion of the issues."

The Justice Department's demand for documents on the company's dealings in Iran is the latest controversy the Houston oil services giant has faced recently. It is under investigation by several government auditors for allegedly charging inflated fees for oil and services in Iraq during the war and in its aftermath, as well as by authorities here and in France for alleged bribes related to work on a gas liquefaction plant in Nigeria when Cheney was chief executive.