From: Rabbi Moshe Sofer
To: Rabbi Shmuel Katz
The question is whether a Kohen who enters a house where a Niddah is present may perform Birkas Kohanim, given a stringency attributed to Sefer HaMiktzaos cited by the Pri Chadash. The Chasam Sofer rules decisively that there is no concern, dismantling the halachic reasoning on multiple grounds, and states that a Kohen who refrains from blessing acts inappropriately by withholding a biblical obligation.
Source: Shu"t Chasam Sofer OC §23