The change, which affects the $144 billion nursing-home industry, was enacted with no public notice or attention.

"This is pretty stunning," said Mark Kosieradzki, a plaintiff attorney in Plymouth, Minn. "Nobody was told. It was just done."

The rule designates state inspectors and Medicare and Medicaid contractors as federal employees, a group usually shielded from providing evidence for either side in private litigation.

The restrictions affect about 16,000 nursing facilities and 3 million residents in the United States. The practical effect is to force litigants to go to greater lengths, including seeking court orders, to get inspection reports or depositions for cases they are pursuing or defending.

"This change hurts nursing-home residents and their families by allowing bad practices to be kept in secret by nursing homes and inspectors," said Eric M. Carlson, an attorney with the National Senior Citizens Law Center in Los Angeles. "Government inspectors have the right to go into nursing homes and investigate, and they learn things that residents and families otherwise could never find out."

The new rule, which was issued in September, generally prohibits state health departments and contractors from participating in private lawsuits involving facilities that are in the federal assistance program without approval by the head of the Department of Health and Human Services.