Passage: Hosenfeld befriended numerous Poles and even made an effort to learn their language. He also attended Mass, received Holy Communion, and went to confession in Polish churches, even though this was forbidden. His actions on behalf of Poles began as early as autumn 1939, when against regulations he allowed Polish prisoners of war access to their families and even pushed successfully for the early release of at least one. During his time in Warsaw, Hosenfeld used his position to give refuge to people, regardless of their background, including at least one politically persecuted anti-Nazi ethnic German, who were in danger of persecution, even arrest by the Gestapo, sometimes by getting them the papers they needed and jobs at the sports stadium that was under his oversight. Hosenfeld surrendered to the Soviets at Błonie, a small Polish city about 30 km west of Warsaw, with the men of a Wehrmacht company he was leading.

Question: what was forbidden in polish churches?
confession