The tax man cometh for big tech.

President Obama's latest budget proposal seeks to close a loophole sheltering overseas business profits from U.S. taxes.

The tax-law change, which has not yet been introduced for a vote to Congress, hopes to collect an extra $210 billion in corporate taxes.

For U.S. companies like IBM ( IBM), Hewlett-Packard ( HPQ), Microsoft ( MSFT), Intel ( INTC), Cisco ( CSCO), Qualcomm ( QCOM) and Juniper ( JNPR), which operate foreign subsidiaries, this could mean bigger tax bills.

"Many U.S. companies with large foreign operations have been able to legally avoid U.S. taxes on their foreign earnings resulting in blended effective corporate tax rates well below the 35% standard U.S. corporate rate," JPMorgan analyst Ehud Gelblum wrote in a note Thursday.

The current offshore tax shelter gives Cisco, Qualcomm and Juniper a big break.

"These companies enjoy low, effective tax rates of 22%, 22%, and 29%, respectively, primarily because a large portion of income is earned overseas and earnings are not repatriated," Gelblum wrote.

Take, for example, Cisco, a major loophole beneficiary. According to the company's most recent quarterly financial filing last month, Cisco has $26.3 billion in cash and investments parked overseas in various subsidiaries. The San Jose, Calif., networking gearmaker holds a mere $3.2 billion in cash in the U.S.

It's no wonder Cisco made a top hundred list with 201 foreign subsidiaries, according to December report by the U.S. Government Accounting Office. Thirty-eight of Cisco's international operations are in what the GAO calls offshore "tax havens or financial privacy jurisdictions" like Barbados, Bermuda, Luxembourg and Switzerland.

Intel stands out in the GAO's tax evasion report. Of the chipmaker's 15 foreign subsidiaries, five were based in the tropical tax-evasion hotspot, the Cayman Islands.

Qualcomm said in a quarterly filing that as of the end of 2008, it had $6.5 billion sitting with at its foreign subsidiaries and $6.6 billion here in the U.S.

So what? Well, in addition to the crushing impact the economy is having on the top line, the bottom lines on some global tech titans could soon feel a tax pinch.

"Under a worst-case-scenario," Gelblum wrote, Cisco and Qualcomm would see a 22% tax rate grow to 35%. This would reduce 2010 earnings by 17%.

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