WASHIGNTON (CBS.MW) - When Toyota added extra duties to Ella Williams' assembly-plant inspection job, she said carpal tunnel syndrome prevented her from handling the additional tasks.

Toyota refused to return Williams to her old job. She sued under the Americans With Disabilities Act, which obligates employers to meet the workplace needs of disabled employees.

The Supreme Court's ruling last week in William's losing case threatens to make it harder for millions of Americans to win accommodations from an employer when physical conditions limit their ability to perform job assignments.

The decision generally narrows the scope of the Disabilities Act by establishing more stringent tests for defining a disability. The issue is not whether a person can perform the specific tasks associated with a job, but rather "whether the claimant is unable to perform the variety of tasks central to most people's daily lives," Justice Sandra Day O'Connor wrote in the unanimous opinion.

"Household chores, bathing and brushing one's teeth" are the types of activities to consider in judging if someone is disabled, the Court established.

It remains unclear exactly what conditions may no longer qualify workers for accommodations under the ADA, or how employers and employees may respond to the Court's decision.

"The ruling is quite specific to carpal tunnel syndrome. It's not at all clear that it has any relation to...psychiatric conditions, for example," said Dr. Mark Levy of the University of California, San Francisco.

A victory for employers?

Many rushed to call last week's court decision a clear victory for employers, because it makes it harder for employees to request special accommodations under the Americans with Disabilities Act.

"It limits the definition of what it means to be disabled, and it reduces employer obligations," said Kathleen Blank, an attorney-adviser with the National Council on Disability.

"People will be discouraged in asking for accommodations in the workplace," she predicted. "Now the employer may scrutinize whether they're disabled or not more intently."

The U.S. Chamber of Commerce praised the decision, and argued it would likely reduce the number of "marginal cases" brought under the umbrella of the ADA statute.

Indeed, the ruling is likely to limit the occurrence of frivolous claims, where unscrupulous employees manipulate the ADA to make their jobs and lives easier, said Kurt Hamrock, a corporate attorney with McKenna & Cuneo LLP in Washington, D.C.

"It will require plaintiffs to think a little longer and a little harder about whether they're disabled before they bring suit."

Yet the pro-ruling camp may be overstating their case in declaring victory, Hamrock said. "It wasn't a slam dunk for the employers. It will reduce a certain category of claims that are being filed."

Blank questioned why employers would rather lose an employee than make an accommodation for them, such as adding a piece of equipment to make their job easier.

"Research has shown that most accommodations are not expensive, costing $500 or less," she said. "If you let someone go because you're not willing to make an accommodation, you have to deal with the cost of brining on someone new."

Americans affected

How many citizens fall under the protection of the Americans With Disabilities Act is uncertain, as few records are kept on claims made under the 10-year-old statute.

When Congress enacted the law, it estimated that about 43 million Americans had a physical or mental disability, O'Connor noted in the court's ruling.

The Administrative Office of the U.S. Courts, which tracks all cases at the federal level, keeps no statistical breakdown of ADA cases, spokesman Dick Carelli said.

Employers further are not required to report actions to any agency when they do make accommodations under the Act, according to Blank.