The U.S. Supreme Court on Wednesday struck down a key pillar of federal campaign finance law by allowing donors to give money to as many political candidates, parties and committees as they wish.

In the latest in a series of decisions by the high court that have given big-money donors more influence in U.S. elections, the justices rejected the overall limits on how much individuals can donate during a federal two-year election cycle.

The ruling — a 5-4 decision with the court's more conservative justices in the majority — could have an immediate impact on the 2014 midterm elections, in which Republicans are likely to keep control of the House of Representatives and are seeking to gain six Senate seats to take over that chamber.