Washington (CNN) The US Supreme Court on Monday refused to take up a case that would have given businesses the right to contribute money directly to candidates.

The high court, in an unsigned order, declined to consider a challenge to a Massachusetts law barring for-profit corporations from donating to political campaigns. In doing so, the justices kept in place a key pillar of campaign finance law and rejected an opportunity to dramatically expand the court's blockbuster Citizens United ruling in 2010 that allowed corporations to spend unlimited sums in candidate elections, as along as the spending remained independent of candidates.

That ruling, and a separate appellate court decision later that year, helped give rise to free-spending super PACs.

The Massachusetts' case was brought by two companies, 1A Auto Inc. and 126 Self Storage Inc., which argued the state's ban on donations from for-profit corporations to candidates and political committees violated both the companies' First Amendment free-speech rights and the Constitution's guarantee of equal protection under the law.

The state, the companies argued, imposes tougher restrictions on for-profit companies than it does on nonprofit corporations and unions. Last year, Massachusetts' highest court upheld the state's ban on corporate contributions to political campaigns, saying it serves to prevent corruption.

Read More