This from Halachically Speaking:
According to some poskim the bread of a non-frum
Jew is also included in the above issur and one is forbidden to eat it. 7
7. Refer to Pischei Teshuva Y.D. 112:1, Kitzur Shulchan Aruch 72:2, Darchei Teshuva 112:5, Kaf Hachaim 11,
Igros Moshe Y.D. 1:45 who are not so convinced. Refer to Orchos Rabbeinu 3:page 79:40 quoting the opinion of the
Chazon Ish. Refer to Yabea Omer Y.D. 5:10, Halichos Olom 7:pages 92-96 in depth. In regard to those who were
is lenient. Also refer to Bishul Yisroel pages 412-413.
Here is the Mahara”m Schick.