"Two people with This Is Rigged have sprayed the words 'the people are mightier than a lord,' the slogan of the Highland Land League, on a painting of King Charles III," This Is Rigged tweeted.
The paint was sprayed on the glass covering, so the painting itself appears unaffected.
"The time has come again when we have to resist, to get our government to stand up to the lairds [lords] who wish to profit off of the world's destruction and the poverty of our communities. This is Rigged will continue to take action until the Scottish government vocally oppose all new oil and gas licenses and secure a fair and fully funded transition for workers to renewable energy," the climate movement added.
This Is Rigged hinted its members paid homage to Scottish feminist Maude Edwards, who slashed a portrait of King George V in 1914.
After committing the act of vandalism, the activists superglued themselves to the floor below the painting
The portrait of King Charles III was painted by Victoria Crowe in the Birkhall estate in Scotland in 2018 and has since been exhibited at the Scottish National Portrait Gallery. The painting depicts the monarch sitting in a chair in front of a window.