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 and President 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. Its function 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 significant responsibilities, such as the power to bring the President before the State Tribunal (impeachment). The current leading party is the Socialist Unity Party (SUP) with 234 out of 460 seats in Sejm and 61 out of 100 seats in Senate. The two debating halls have designated seats for the deputies, senators and the Marshals, equipped with voting devices, used by the deputies and senators to vote.