China has attacked US plans to sell $6.4bn worth of arms to Taiwan. China suspended military exchanges with Washington after the plan was announced.
It has not yet said what sanctions it might impose on the firms, which are supplying Taiwan with missiles, Black Hawk helicopters, information systems and two minehunters.
Boeing said it had not received any official notice of sanctions, saying "this is a government-to-government issue".
The US aerospace and defence firm has contracted hundreds of millions of dollars worth of parts for its 787 Dreamliner to Chinese suppliers, and more than a third of its aircraft have major parts made or assembled in China. More than half of the aircraft flown by China's airlines are Boeing or McDonnell-Douglas jets, and just keeping them maintained and supplied with parts is a huge part of Boeing's global business. (Source: BBC.co.uk, Feb 1, 2010).