Lawmakers and the Obama administration have struggled to come up with a solution. In his latest budget proposal, President Obama calls for imposing a 19 per cent tax on foreign profits -- significantly lower than the current rate.
But there is little political momentum to address the issue during the 2016 presidential election cycle and Republicans and Democrats remain split on an approach.
"Stashing money offshore to avoid US taxes is hardly a victimless crime," said Bob McIntyre, director of Citizens for Tax Justice.
"Every dollar shifted to an offshore tax haven means less federal revenue to pay for the infrastructure, education and other public services that help our economy grow."
Business leaders have said that companies have few choices as long as the corporate tax rate remains high.
Many have called for broad tax reform. In the meantime, companies' unrepatriated income is widely expected to continue to grow.
Last year, Apple's unrepatriated profits reached US$200 billion, up from US$157 billion in 2014 and $111 billion in 2013, according to the report.
Microsoft's overseas profits stockpile reached US$108 billion last year, according to Citizens for Tax Justice.
Pfizer's unrepatriated income reached $193 billion last year compared with US$175 billion the previous year. The company announced last November that it would merge with Botox-maker Allergan and move its headquarters to Ireland. The deal is expected to lower Pfizer's corporate tax rate to 17 or 18 per cent, compared with its current effective 25 per cent rate. But it would also make it easier for the pharmaceutical giant to gain access to its overseas profits and could help it save about US$35 billion in taxes.
Wisconsin manufacturer Johnson Controls announced last month that it would merge with Tyco International and also move its headquarters to Ireland.
That is expected to save the company US$150 million a year in taxes and make it easier for it to access US$8 billion in unrepatriated income.