The parliament of Poland is the bicameral legislature of Poland. It is composed of an upper house (the Senate) and a lower house (the Sejm). Both houses are accommodated in the Sejm complex in Warsaw. The Constitution of Poland does not refer to the Parliament as a body, but only to the Sejm and Senate. Members of both houses are elected by direct election, usually every four years. The Sejm has 460 members, while the Senate has 100 senators. To become law, a bill must first be approved by both houses, but the Sejm can override a Senate refusal to pass a bill. On certain occasions, the Marshal of the Sejm summons the National Assembly, a joint session of the members of both houses. It is mostly ceremonial in nature, and it only convenes occasionally, such as to witness the inauguration of the President. Under exceptional circumstances, the constitution endows the National Assembly with great responsibilities and powers, such as to bring the President before the State Tribunal (impeachment). The current leading party in the Sejm is the Law and Justice (PiS) party with 226 out of 460 seats in Sejm whereas with 48 out of 100 seats in Senate (thus controlled by opposition parties, currently: Civil Coalition, The Left, and Polish People's Party). The two debating halls have designated seats for the deputies, senators and the single Marshal (speaker) of each. Senators and deputies are equipped with voting devices. After election deputies and senators will remain or splinter into deputy or senatorial groupings, or have no affiliations and sit as "independents". In both chambers, there are two formal sizes of groups: Clubs (kluby, klub () which are the entire party groups of the elected, where none have splintered away or defected to another klub) and circles (koła, koło ()). The primary difference between these is the degree of right to join and contribute to the relevant Seniors' Konwent (Konwent Seniorów), the procedural committee that determines the drafting of agendas and chamber workings.