Tarred with the same brush

A metaphor for being found guilty of the same misdeeds of another, especially unjustly, that dates from the early 19th century. The origin is the figurative meaning of the word tar, meaning to dirty or defile (as with tar) and dates, according to the OED, from 1612. Black, sticky pitch or tar was and still is used as a construction and insulation material and is generally applied with a brush. See also touch of the tarbrush.