The Switzerland ETS began with a voluntary phase as an alternative option to the CO2 levy on fossil fuels. Revised regulations entered into force in January 2013. The system subsequently became mandatory for large, energy-intensive entities, while medium-sized entities may join voluntarily. The ETS applies to industrial entities, largely comprising companies from the cement, chemicals, pharmaceuticals, paper, refinery, or steel sectors. It now covers about 11% of the country’s total GHG emissions.