Story highlights Organizers project holograms of marchers in front of lower house of parliament

They are opposing a new law that they say criminalizes citizens' right to protest

(CNN) Thousands of people marched past a Spanish parliament building in Madrid over the weekend weekend to protest a new law that they say endangers civil liberties.

But none of them were actually there.

The demonstrators were taking part in what organizers described as the world's first hologram protest.

They used equipment to project the marchers' holographic forms in front of the Congress of Deputies, the lower house of the national parliament, for about an hour on Friday night.

But the ghostly demonstration was more than just a technological stunt. It also highlighted some of the constraints in the new Citizen Safety Law, which critics have dubbed "the Gag Law."

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