WASHINGTON (Reuters) - U.S. civil rights groups filed a lawsuit on Thursday to have a white nationalist rally in Virginia moved back to its original venue, saying that city officials’ last-minute decision to shift the event violated organizers’ rights.

The suit by the American Civil Liberties Union and the Rutherford Institute, a civil liberties organization based in Charlottesville, Virginia, comes ahead of Saturday’s “Unite the Right” rally in Charlottesville, which city officials expect to draw thousands of participants and counter-demonstrators.

The city’s decision this week to shift the event from the downtown Emancipation Park violates organizers’ constitutional rights of freedom of speech, assembly and petition, according to the 16-page lawsuit, filed in U.S. District Court in Charlottesville.

The Constitution “prohibits the government from blocking a protest based on its content or viewpoint, or based on how the government anticipates others will respond to the protest,” the complaint said.

Miriam Dickler, a spokeswoman for the city of Charlottesville, said the city did not comment on litigation.

Jason Kessler, a freelance journalist, organized the rally to protest Charlottesville’s decision to rename the park, previously called Lee Park, and to remove a statue of Confederate General Robert E. Lee there. He was granted a permit in June, the lawsuit said.

But Charlottesville officials shifted the rally on Monday to McIntire Park, a larger site a mile (1.6 km) from Emancipation Park. In a statement, city manager Maurice Jones cited safety concerns and the large number of people expected to attend the rally.

Statues and monuments to Confederate or pro-slavery figures have become flash points of protests between supporters who see them as part of American or regional heritage and those who call them racially insensitive.

About two dozen people were arrested in July after a rally by the Ku Klux Klan in Charlottesville, home of the University of Virginia’s flagship campus, to protest the decision to move the Lee statue. Torch-wielding white nationalists also demonstrated against the removal in May.

The Confederacy was made up of states that attempted to preserve slavery in the South and secede from the United States in the Civil War of 1861 to 1865.