WASHINGTON -- In a decision that gives unions broader authority to organize about 250,000 workers at more than 400 Indian casinos, a federal court on Friday ruled tribal gambling operations are not exempt from the National Labor Relations Act.

The U.S. Circuit Court of Appeals in Washington, D.C., denied an appeal from the San Manuel Band of Mission Indians in California, which argued its sovereignty was violated in 2004 when the National Labor Relations Board asserted its jurisdiction in a labor dispute at the tribe's casino.

In an opinion written by Judge Janice Rogers Brown, the court ruled the operation of a casino "is not a traditional attribute of self-government."

Secondly, the vast majority of the casino's employees and customers are not members of the San Manuel Band of Mission Indians, Brown wrote.

"For these reasons, the tribe is not simply engaged in internal governance of its territory and members, and its sovereignty over such matters is not called into question," Brown wrote.

The other two judges who heard the case -- Merrick Garland and Stephen Williams -- joined in the opinion.

In addition, the court rejected the tribe's claim that the Indian Gaming Regulatory Act of 1988 prevents the federal government from regulating tribal casinos.

The tribe cited its compact with California, and argued that the 1988 federal law gives tribes and states a primary role in regulating Indian gambling activities.

But the court answered that the tribe "reads too much into IGRA."

"IGRA certainly permits tribes and states to regulate gaming activities, but it is a considerable leap from that bare fact to the conclusion that Congress intended federal agencies to have no role in regulating employment issues that arise in the context of tribal gaming," Brown wrote.

Ernest Stevens, chairman of the National Indian Gaming Association which is the chief lobbying arm of tribal casinos in Washington, said tribal governments may appeal the decision or seek new legislation.

Stevens charged that the court mistakenly equated Indian gaming with commercial gaming.

"Indian gaming is an exercise of inherent tribal sovereignty akin to the exercise of state sovereignty behind state lotteries," Stevens said in a statement.

The San Manuel Band of Mission Indians casino is located about 60 miles east of Los Angeles and is considered one of the largest businesses in San Bernardino County.

The casino includes a 2,300-seat bingo hall and employs about 1,400 workers.

In January 1999, UNITE HERE -- then known as Hotel Employees Restaurant Employees -- filed an unfair labor practice charge against the casino with the National Labor Relations Board.

UNITE HERE claimed it was not allowed a chance to organize the casino's workers while Communications Workers of America -- the union that now represents most of the casino's workers -- was given access by the tribe to its casino property.

In May 2004, the National Labor Relations Board issued a cease-and-desist order that required the tribe to give UNITE HERE access to the casino and to post notices in the casino describing rights of the employees under the National Labor Relations Act.

The tribe appealed to the U.S. Circuit Court of Appeals in Washington, D.C.

NLRB spokeswoman Patricia Gilbert declined to comment on Friday's ruling.

Calls to the San Manuel Band of Mission Indians and Los Angeles attorney Jerome Levine, who represented the tribe in arguments before the court in November, were not returned.

A call to Las Vegas attorney Richard McCracken, who represented UNITE HERE, was not returned.