Responsa к Дварим 6:7

If not for the fact that I do not usually dispute earlier authorities unless there is a great authority to support me, I would incline toward leniency and in favor of reciting blessings with an uncovered head. Even the recitation of Shema is permitted, for it states in Midrash Rabba (Vayikra §27): R. Berekhya said: A flesh-and-blood king sends his charter to the province, what do they do? All residents of the province stand up, uncover their heads, and read it with fear, awe, trembling, and perspiration. But the Holy One, blessed be He, says to Israel: Recite the Shema, My charter. I do not trouble you to read it standing or with your heads uncovered. This clearly implies that it is not forbidden to uncover one’s head; rather, He did not impose [an uncovered head] as a stringency. But what can I do? They have already ruled this to be forbidden.