The formula is not an official law, but rather an agreement amongst the rather large coalition of four parties. After the 2003 general elections, the formula was modified, giving two seats to the SVP at the expense of the CDPP.
After the election of Eveline Widmer-Schlumpf to the federal council in Fall 2007, she was expelled from the UDC, because she accepted to take the seat of Christoph Blocher, the inofficial leader of the UDC party. Samuel Schmid followed her, as he, too, was no longer supported by his own party. They leaded the establishment of the new Conservative Democratic Party of Switzerland (BDP/PBD). Due to this change, the two seats from the UDC now belong to the PDB, although it has only a handful of seats in the parliament.
The formula
Conservative Democratic Party of Switzerland (BDP/PBD): Two seats.
Free Democratic Party (FDPP/PRD/PLR/PLD): Two seats.
Social Democratic Party (SPS/PSS): Two seats.
Christian Democratic People's Party (CVP/PDC/PPD/PCD): One seat.
