IRA slogans have been written across a new memorial to 10 Protestant workmen shot dead in South Armagh.
The Kingsmills monument commemorates the victims of the IRA ambush in 1976.
Ulster Unionist Assembly member Danny Kennedy, who is at the scene with some of the dead men's families, said: "It is quite reprehensible that people would stoop to this level and seek to further injure the thoughts and memories of the families involved."