From: Rabbi Moshe Sofer
To: Unknown recipient
A dying childless man's community sought to write a get on the second day of Shavuos to prevent his wife from being bound to levirate marriage. The Chasam Sofer emphatically upholds the prohibition, affirming that Yom Tov Sheni's sanctity cannot be overridden for writing a get.
Source: Shu"t Chasam Sofer OC §145