The American taxman has hit mobile phone maker Motorola with a $500m (£273m) bill, claiming the firm underpaid between 1996 and 2000.
Motorola said the internal revenue service had demanded the payment after completing an audit of its tax returns in June.
Dwindling payments have led the US government to crackdown on corporations dodging tax. A government report in April found that almost two-thirds of American companies paid no tax between 1996 and 2000 even as the economy was booming.
Motorola said it disputed the findings and would appeal. The IRS has questioned Motorola's accounting for "transfer pricing", the prices at which units in the company sell goods or services to one another. According to the IRS, Motorola should have reported an additional $1.4bn profit over the period.
The bill is a blow for Motorola, which has been recovering after a difficult few years. It reported profits of $800m in the most recent quarter, up from $112m a year ago.
