Instead of moving in to clear the camp, as had been expected, police concentrated on clearing several hundred protesters who had spilled into the street so morning rush-hour traffic would not be affected.
Hours later, several demonstrators asked a federal judge for an injunction against the city.
The civil rights complaint contends that Mayor Antonio Villaraigosa usurped the City Council's authority when he set a deadline of 12:01 a.m. Monday for the tent-dwellers to disband.
The council passed a resolution of support for the occupiers in October that effectively allowed them to remain on the lawn despite a city ban on overnight camping, the complaint argued.
"The City Council welcomed them with open arms and said they could stay as long as they want," said Jim Lafferty, executive director of the Los Angeles chapter of the National Lawyers Guild.
"The mayor simply does not have the authority to do this," he said.
The city attorney's office had not been served with the complaint and could not comment on it, spokesman John Franklin said. However, he said the city was prepared to oppose any injunction.
"We'll be in court," he said.
Constitutional law experts were skeptical of the injunction's chances.
The U.S. Supreme Court has held that while public parks can be used for protests, they are for the use of all people, not just one group, and that governments can restrict how a park is used for free speech purposes.
"Parks are open to free speech, but that's not a place they can authorize as their own home," said Eugene Volokh, a First Amendment expert at the University of California, Los Angeles, School of Law.
Mulvihill reported from Philadelphia. Associated Press writers John Rogers and Andrew Dalton in Los Angeles, Kathy Matheson in Philadelphia, and Glenn Adams in Augusta, Maine, contributed to this report.
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