according to one source:
The phrase "speaking truth to power" goes back to 1955, when the American Friends Service Committee published Speak Truth to Power, a pamphlet ii at proposed a new approach to the Cold War. Its title, which came to Friend Milton Mayer toward the end of the week in summer 1954 when the composing committee finished work on the document, has become almost a cliche; it has become common far beyond Quaker circles, often used by people who have no idea of its origins. (One current example: Anita Hill entitled her memoir of her sensational charges of sexual harassment against Supreme Court nominee Clarence Thomas, Speaking Truth to Power.)
To speak truth to power sounds so much like an integral part of Quakerism that some modem Friends have simply assumed the phrase goes back to the seventeenth century rather than arriving late in the middle of ours. It reflects what many contemporary Friends would like to believe is the characteristic Quaker stance toward political authority, hallowed in practice if not the exact words. Yet in its origins it was a political statement, entitling an explicitly political document.
Our confusion about this phrase and what we think it represents is what makes Hans A. Schmitt’s book, Quakers and Nazis: Inner Light in Outer Darkness such relevant reading for Friends. A Frankfurt-born historian, who retired at the beginning of this decade from a productive career at the University of Virginia, Schmitt has told a compelling story about how the tiny German Yearly Meeting responded to monstrous evil.
http://www2.gol.com/users/quakers/living_the_truth.htm