"The no-holds-barred flow of seven- and eight-figure checks, most undisclosed, into super-PACs; they fundamentally threaten to overwhelm the political process over the long run and drown out the voices of ordinary citizens," Obama wrote in a chat session on the social news Web site Reddit.
"We need to start with passing the  Disclose Act that is already written and been sponsored in Congress -- to at least force disclosure of who is giving to who," Obama wrote. "We should also pass legislation prohibiting the bundling of campaign contributions from lobbyists.
"Over the longer term, I think we need to seriously consider mobilizing a constitutional amendment process to overturn Citizens United (assuming the Supreme Court doesn't revisit it)," he wrote.
"Even if the amendment process falls short, it can shine a spotlight of [sic] the super-PAC phenomenon and help apply pressure for change," he wrote.
This was the first time Obama, a former constitutional law professor, voiced support for such an amendment since the Supreme Court's Jan. 21, 2010, ruling in Citizens United vs. Federal Election Commission that said the First Amendment allowed for unlimited corporate and union spending on electioneering communication.
Obama campaign senior strategist David Axelrod told New York magazine in June Obama intends, if he is re-elected, to have his administration "use whatever tools [are] out there, including a constitutional amendment, to turn this back."
Obama condemned the ruling in his 2010 State of the Union address six days after the court handed it down.
"With all due deference to separation of powers, last week the Supreme Court reversed a century of law that I believe will open the floodgates for special interests -- including foreign corporations -- to spend without limit in our elections," he said.
Justice Samuel Alito was seen frowning and mouthing "not true" when Obama spoke about the ruling.
Obama allies run the Priorities USA Action independent expenditure political action committee in support of Obama's re-election, but it refuses to accept anonymous donations.