The Senate is the upper house of the bicameral Parliament of Australia, the lower house being the House of Representatives. The composition and powers of the Senate are established in Chapter I, Part II of the Australian Constitution. There is a total of 76 senators; 12 senators are elected from each state, regardless of population. Each of the two autonomous internal territories has two senators. Senators are popularly elected under a single transferable vote system of proportional representation. There is no constitutional requirement for the election of senators to take place at the same time as those for members of the House of Representatives, though the government usually tries to synchronise election dates. Senators normally serve fixed six-year terms, unless the Senate is dissolved earlier in a double dissolution. Following a double dissolution half the state senators serve only three-year terms. The term of the territory senators expires at the same time as there is an election for the House of Representatives. Unlike upper houses in most parliamentary systems, the Senate is vested with significant power, including the capacity to block legislation initiated by the government in the House of Representatives, making it a distinctive hybrid of British Westminster bicameralism and US-style bicameralism. The present Parliament was elected at the 2013 election, and is the 44th Federal Parliament since Federation. The six-year term of the 36 state senators who were elected commenced on 1 July 2014. In the current Senate, the Liberal/National Coalition government holds 33 seats and the Australian Labor Party opposition has 25 seats. The crossbench of 18 consists of ten Greens seats, two Palmer United Party seats, with one each for the Australian Motoring Enthusiast Party, the Liberal Democrats, the Family First Party, and three independents, Nick Xenophon, John Madigan and Jacqui Lambie. The Coalition requires six non-Coalition Senators to pass legislation.