California and 11 other U.S. states were allowed to continue to grant in-state college tuition to high school graduates who are illegal immigrants under a new Supreme Court decision.

The top U.S. court in Washington rejected an appeal from a conservative group which called the tuition grant an illegal "preferential treatment" for illegal immigrants and a violation of federal immigration laws, The Los Angeles Times reported Monday.

The group cited a little-known 1986 law provision that bars states from giving "any postsecondary benefit" to an "alien who is not lawfully present in the United States on the basis of residence within a state."

The court's action is not an official ruling, but it leaves in place laws in 11 other states that permit illegal immigrants to obtain in-state tuition, including Illinois, Kansas, Maryland, Nebraska, New Mexico, New York, Oklahoma, Texas, Utah, Washington and Wisconsin.

Under a 2001 law, California gives in-state tuition to a qualified student who attended a high school in California for three years and graduated.

Last year, in the first ruling of its kind, the California Supreme Court said the state's policy did not conflict with federal law because the tuition benefit turned on a student's high school graduation, not his or her residency.

Overall, the state said about 41,000 students last year took advantage of this special tuition rule, but the vast majority of those were students at community colleges.

The 10-campus University of California (UC) system said 2,019 students paid in-state tuition under the terms of the state law in 2009. Of these, about 600 were believed to be illegal immigrants.

Another 12 states have explicitly refused to grant in-state tuition to illegal immigrants. For its part, the federal government -- through the Clinton, Bush and Obama administrations -- has taken no steps to enforce the federal provision, the report said.