بسم الله الرحمن الرحيم
A person who keeps his beard less than one fist he is transgressor. Salah shall be makrooh tahrimi behind him. The post of imam is the deputyship of the holy Prophet Muhammad (may peace and blessings of Allah be upon him). It is shameful act that imam cuts his beard while being on such high post. You should make the imam understand it. If he stops from cutting his beard then alright otherwise that imam should be sacked and some pious person who follows the Shariah completely should be appointed as imam.
Allah knows Best!
Darul Uloom Deoband
This answer was collected from the official ifta website of Darul Uloom Deoband in India.