Democratic U.S. Sen. Al Franken slammed a Supreme Court decision that could give wealthy donors more influence over federal elections.

The justices ruled Wednesday that limits on the total amount of money donors can give to all candidates, committees and political parties are unconstitutional. The decision leaves in place the base limits on what can be given to each individual campaign.

In a statement issued by his office, Franken called the decision "terrible."

The decision in McCutcheon v. Federal Election Commission marks the latest round in the bitter national debate over the role of money in American politics.

"Ordinary people in Minnesota and around the country don't have the luxury of pouring millions into political campaigns, and our democracy can't function the way it's supposed to when their voices are drowned out by a flood of corporate money," Franken said. "Many of us believe that the measure of a democracy's strength is in votes cast, not dollars spent – and for us, there's nothing to celebrate today."

The McCutcheon ruling could be the most important campaign-finance decision since the Supreme Court 2010 Citizens United v. Federal Election Commission ruling, which allowed corporations and unions to spend unlimited amounts independently to influence elections.

Franken has backed a constitutional amendment overturn Citizens United.

"Ever since the Supreme Court issued its decision in Citizens United in 2010, we've seen hundreds of millions of often completely anonymous dollars flood into our electoral process," Franken said. "These rulings give wealthy, well-funded corporate interests undue influence, access and power."