There are also an estimated 1 million legal residents — immigrants with green cards — who are waiting for their spouses' paperwork to be processed, according to Paul Donnelly of Reform the Rebate, a group trying to push Congress the change the rule. The IRS doesn't keep numbers of how many of that group are cut out of the rebate because they filed jointly.

And many of the 600,000 to 800,000 highly skilled immigrants on work visas in the U.S., like Shelat, have found themselves in the same position, having married a foreigner.

"My friends, my co-workers, everyone is getting this, but not me," said Ranjeet Kumar, a software engineer who has been working in Silicon Valley for eight years.

Kumar's wife is in the U.S. legally but her status still doesn't allow her to work or apply for a Social Security number. The couple filed taxes jointly but won't qualify for the $1,200 rebate other eligible couples would get.

"I know they want to exclude illegal immigrants — but I'm not illegal, I've done exactly what I was supposed to do," Kumar said.

Members of the Federation for American Immigration Reform lobbied against a version of the bill that didn't require a Social Security number for the rebate, worried about the prospect of illegal immigrants receiving checks. Spokesman Ira Mehlman said the exclusion of legal immigrants and Americans married to noncitizens was an unintended consequence.

"If you're serving abroad and haven't been able to file the paperwork, they should make an exception," he said. "If one spouse is a citizen, is here legally and is filing, they should probably be entitled."

Many of the couples snagged by this provision weren't aware that filing taxes using the foreign spouse's IRS-issued Taxpayer Identification Number instead of a Social Security number would cut them out. On April 14, the day before the tax deadline, the IRS clarified the situation on its Web site.

"They can file separately, though that may not necessarily be to their benefit," said Eric Smith, an IRS spokesman.

Tax advisers said even if these couples had known, frequently the financial benefits of filing jointly outweigh the maximum of $600 that the spouse with the Social Security number could get by filing separately.

But many of these couples feel they shouldn't have to choose since they've been working legally and paying taxes.

Sheila Reed, who works at Command Navy Region Europe in Naples, Italy, said she filed taxes together with her husband, who still uses the IRS Taxpayer Identification Number.

"I don't feel this is fair because I pay taxes like any other U.S. citizen," she told Stars and Stripes, a newspaper published for the U.S. military and other Department of Defense personnel. "It's not right. I have three kids."