Legislative power is vested in the unicameral Riksdag with 349 members. General elections are held every four years, on the second Sunday of September. Legislation may be initiated by the Government or by members of the Riksdag. Members are elected on the basis of proportional representation to a four-year term. The internal workings of the Riksdag are, in addition to the Instrument of Government, regulated by the Riksdag Act (). The fundamental laws can be altered by the Riksdag alone; only an absolute majority with two separate votes, separated by a general election in between, is required.