In this paper, Michael Sudduth blows this charge out of the water.
Sudduth quotes Calvin:
That Sarbonic dogma, therefore, in the promulgation of which the Papal theologians so much pride themselves, “that the power of God is absolute and tyrannical,” I utterly abhor. For it would be easier to force away the light of the sun from his heat, or his heat from his fire, than to separate the power of God from His justice. Away, then, with all such monstrous speculations from godly minds, as that God can possibly do more, or otherwise, than He has done, or that He can do anything without the highest order and reason. For I do not receive that other dogma, “that God, as being free from all law Himself, may do anything without being subject to any blame for doing so.” For whosoever makes God without law, robs Him of the greatest part of His glory, because he spoils Him of His rectitude and justice. Not that God is, indeed, subject to any law, excepting in so far as He is a law unto Himself. But there is that inseparable connection and harmony between the power of God and His justice, that nothing can possibly be done by Him but what is moderate, legitimate, and according to the strictest rule of right. And most certainly, when the faithful speak of God as omnipotent, they acknowledge Him at the same time to be the Judge of the world, and always hold His power to be righteously tempered with equity and justice. (Emphasis Sudduth's)