The rally focused on plans by Spain’s left-wing government to change the citizen security law, known as the “gag law”, passed in 2015 under the previous right-wing administration at the height of the anti-austerity protests.

The reform bill aims to bring the law in line with a Constitutional Court ruling that authorisation to use images of police was “unconstitutional” because it amounted to “prior censorship”.

Waving Spanish flags and union banners, the protesters, accompanied by senior right-wing politicians, marched to the interior ministry in a rally called by Jusapol, an umbrella organisation from which emerged the police and Guardia Civil unions.

They say such reform would remove protection from police and security forces, endanger public security and reduce operational ability to stop violent demonstrations.

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“We say no to this reform. We believe the law must be adapted to current times and must be reformed, but we must never trample the rights of those responsible for security who work with this law every day,” Jusapol president Miguel Ángel Gómez told reporters.

Speaking at the march, opposition leader Pablo Casado, who heads the right-wing Popular Party, said he fully supported the protesters’ demands.

“Every day four police officers are assaulted and this is absolutely intolerable,” said Casado, urging Prime Minister Pedro Sanchez “to listen to the street and to the thousands of police who have risked their lives to defend Spanish democracy and freedom.”

“It is extraordinary that for the first time in our democracy, those who risk their lives to protect us have to demonstrate because they are left unprotected,” he said earlier.

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Other right-wing politicians also joined the march, among them Santiago Abascal, leader of the far-right Vox party and Ines Arrimadas, head of the centre-right Ciudadanos party.

“Basically, what this law does is to remove protection from the police and criminalise them, casting doubt on them and favouring those attacking them,” said Arrimadas.

“We are tired of the fact that in Spain criminals have more protection than the police and those who obey the law.”

Under the current law, the unauthorised use of images of police officers that could endanger their safety is a serious offence, with offenders risking fines of €600 to €10,400.

The reforms also propose changes to the fines, which would be proportional to the offenders’ income, as well as to riot control equipment with possibly the least harmful means to be used.