Following a slew of attacks in which climate activists splashed soup and other substances on iconic pieces of art, the National Gallery in London is banning liquids and enacting a number of other security measures.

Starting Friday, visitors to the free museum in the United Kingdom will not be allowed to enter with any liquids except for baby formula, expressed milk or prescription medicines. They will also have to walk through metal detectors and have their bags inspected to access the building, with the museum asking visitors to bring as few items with them as possible.

“The collection we hold is irreplaceable and with each attack we have been forced to consider putting more barriers between the people and their artworks to preserve these fragile objects for future generations,” the art museum said in a statement. “Unfortunately, we have now reached a point where we have been forced to act to protect our visitors, staff and collection.”

The ban on bringing liquids includes bottled water, the museum said, while noting that free tap water was available to visitors inside the museum.

Over the past two years, activists around the world have symbolically defaced iconic landmarks and artwork to bring attention to their cause, everything from slopping soup on the Mona Lisa in Paris to spraying orange paint on Stonehenge.

While many of these demonstrations began as climate protests – Just Stop Oil flinging tomato soup on Vincent van Gogh’s “Sunflowers” in London and members of climate activist group the Last Generation throwing mashed potatoes on Claude Monet’s “Les Meules” in Germany – protesters have recently been targeting artwork to call for their governments to stop supplying Israel in its war in Gaza.

While the majority of these demonstrations do not appear to have harmed the actual artwork – many of the pieces were protected behind glass – officials with the National Gallery in London said some of the targeted pieces suffered physical damage. Prosecutors said that the two Just Stop Oil activists involved in the “Sunflowers” incident in 2022 had caused £10,000, or $13,400, in damage to the 17th-century Italian frame surrounding it. Mere hours after those activists were sentenced to jail time last month, three more protesters splattered soup on the painting once again – one of two attacks at the National Gallery over the past few weeks.

Since July 2022, the museum has been the site of five separate attacks, which has caused “distress to visitors and staff alike,” the museum said in a statement.

The National Museum Directors’ Council published an open letter on Oct. 11 calling for an end to such demonstrations. “Whilst we respect the right for people to protest, and are often sympathetic to the cause, these attacks have to stop,” the letter reads. “They are hugely damaging to the reputation of UK museums and cause enormous stress for colleagues at every level of an organization, along with visitors who now no longer feel safe visiting the nation’s finest museums and galleries.”

The council acknowledged that the world is “currently in a very dark place, but these demonstrations now need to be taken away from our museums and galleries so that they can continue to provide light and solace to all.”

Just Stop Oil responded with another open letter a few days later: “These actions cause small amounts of damage and disruption to bring to attention the enormous damage and destruction that our government is supporting,” the group wrote. “Today you take issue with soup and stickers, but tomorrow you will contend with rising waters in the Thames and deadly heat waves in the city. People disrupt museum and gallery spaces to break the illusion that everything is fine. We need institutions to confront their responsibilities at this time – head on.”

The group asked to meet with the National Museum Directors’ Council at the National Gallery. “We’ll leave the soup at home,” the group said.