 However, a by-election need only be called within a reasonable time, and the Prime Minister has discretion to determine when it should be held.The law provides that a by-election need only be called in a GRC if all the MPs in the constituency vacate their seats.It has been argued that the law should be amended, otherwise electors living in a GRC where a vacancy has arisen will lack parliamentary representation, and with a missing MP the remaining MPs may find it difficult to deal with constituency matters.