It appears that FDR's attorney general put pressure on the post office to revoke Coughlin's 2nd-class mailing privileges. In the end, the privileges weren't revoked, but (due in part to FDR putting pressure on the Catholic church itself), the bishopry commanded Coughlin to restrict his activities to local ministry.
Father Coughlin was a strong supporter of FDR dating back to when he was Governor of New York. It is only when he broke with FDR in 1936 that he started having problems.
https://en.wikipedia.org/wiki/Charles_Coughlin#Cancellation_...
It appears that FDR's attorney general put pressure on the post office to revoke Coughlin's 2nd-class mailing privileges. In the end, the privileges weren't revoked, but (due in part to FDR putting pressure on the Catholic church itself), the bishopry commanded Coughlin to restrict his activities to local ministry.