Rav David Yosef from the Torah Sages Council of the Shas (ultra-orthodox Sephardic) party has issued a proclamation to his students. In it he calls anyone who does not wear a mask "a walking time bomb."
Rav Yosef likens someone who does not wear a mask to a "rodef," a term in Jewish law for someone who intends to murder another person. In such a case, it is permissible to kill the rodef.