Back in June 2013 Mark Udall sponsored a Bill to amend the constitution to allow Congress and the States to limit Individuals, Corporations, and artificial entities that wish to donate money to elections or advertising. Im sure one of my colleagues may agree with this but this is clearly a round about since the 2010 decision. From the NRA:
In January 2010, the U.S. Supreme Court handed down a key decision in the case of Citizens United v. Federal Election Commission. The decision removed unconstitutional restrictions on the ability to speak freely at election time of grassroots groups like NRA and others. But now, some are trying to reverse the decision–and while they recognize that they must amend the Constitution to do so, their amendment would gut the First Amendment rights of organized political groups as we know them.
This amendment has some far reaching effects depending who is in power. Then they can control who can spend what and where. You can read the text of the resolution here Read More
The NRA has more on this here