Halliburton, in trouble over alleged over-charging for Iraq contracts, is being probed for its deals in Iran.
Did Halliburton comply with both the letter and the spirit of the law?
A US grand jury has demanded documents relating to contracts in Iran - subject to US sanctions - by a Halliburton subsidiary based in the Cayman Islands.
The firm, which used to be run by US Vice-President Dick Cheney, said it was certain the deals were legal.
Another unit, KBR, is being probed over Iraq, while other investigations are examining deals in Nigeria.
KBR ex-chairman Jack Stanley had his consultancy contract with Halliburton torn up last month as a result of the Nigeria affair, which is under review by the US stock market regulator.
The Iran investigation is now with the Justice Department, having started in the US Treasury's Office of Foreign Assets Control - responsible for enforcing sanctions - in 2001.
Halliburton's Iran dealings constitute only a tiny fraction of its overall finances - about 0.5% of its $16.3bn 2003 turnover, according to the most recent annual report.
The multi-billion dollar Iraq contracts under scrutiny after allegations of sweetheart deals and overcharging are worth much more.
And Halliburton is at pains to say that its Caymans subsidiary, Halliburton Products and Services Ltd, was operating in compliance with the relevant laws and rules.
But the probe comes as the use of offshore "tax havens" by large US corporations risks becoming an election issue.
Politicians from across the party divide in the US have spoken out against firms which get government contracts despite being headquartered overseas for tax reasons.
Financial scandals such as Enron, Worldcom and Parmalat centred on the use of the Caymans and other subsidiaries to hide losses.
Halliburton came under fire earlier this month for the Iran deals, with critics charging that they abused the spirit - if not the letter - of sanctions banning US firms from working in Iran.