Karen Marie Christensen (3 February 1871, Kregme – 14 September 1945, Copenhagen) was a Danish trade unionist, women's rights activist and politician. She founded the first union for maids in Denmark, serving as the chairman of the Danish Maid Unions (Danish: Tjenestepigeforeninger i Danmark) from 1904 to 1927 and the leader of its trade school, Københavns Tjenestepigeforenings Fagskole (later Husassistenternes Fagskole), from 1906 to 1938. Christensen's primary goal was to obtain stable pay and better working conditions for domestic workers in Denmark. In 1904, she became the first working-class woman to sit on a Danish government commission, which was charged with reexamining the 1854 Tyendeloven (Servants Law).
Christensen was also active in the women's suffrage movement, playing a significant role in ensuring that the vote was also extended to servants. She sat on the Copenhagen municipal council between 1917 and 1921, as a member of the Social Democrats.