'In 2010, the landmark case filed by Citizens United changed the rules regarding corporate campaign expenditures. This ruling made it legal for corporations and unions to spend from their general treasuries to finance independent expenditures. Direct corporate and union contributions to federal campaigns, however are still prohibited.'
'The 2010 election marked the rise of a new political committee, dubbed "super PACs," and officially known as "independent-expenditure only committees," which can raise unlimited sums from corporations, unions and other groups, as well as individuals. [...] Super PACs are not allowed to coordinate directly with candidates or political parties since they are "independent".'