The Regalian Unionism Party is the ruling political party of the Regalian Empire. It has been in power since 1766 after the Regalian Emperor switched his religion from Paganism to Unionism. Under the Edict of Rightful Loyalty all political parties must be ruled by a member of the religion the same as the emperor. The Druid Council was invalid and was disbanded but some members were arrested for not converting and were accused as heretics by the Regalian Church of Unionism.
The Regalian Unionism Party often shortened to RUP is led by the Chancellor and the Pope they are a member of the Imperial Council. Other political parties can voice their opinions but not vote any proposals on opposing the Emperor is seen as heresy and many political parties have been disbanded.
In truth the Regalian Church and Royal Family govern the party and mainly only members of nobility are MP's of the House of Lords.