A Wellington café owner says a message of 'thanks' to Green Party MP Jeanette Fitzsimons that caused outrage online has been misinterpreted.

Jeanette Fitzsimons, who ushered the Greens into existence and led them into Parliament in the late 1990s, died last week after suffering a fall on the organic farm she owned.

Her passing was mourned by political friends and foes alike, praising her dedication to the environment above all else.

Warren Johnson, owner of Café Villa in Ngaio, Wellington, marked it with a message on a blackboard that graces the side of the building facing the street, writing: "Jeanette Fitzsimons has died. Thank you."

Some locals were horrified.

"Whatever your political persuasion, this is unacceptable," wrote Twitter user @irritable_ish, with a photo of the blackboard.

"What on earth were you thinking, Café Villa in Ngaio? Cold, mean, crass."