The focus of the case will be on whether two conservatives, Chief Justice John Roberts and Justice Samuel Alito, are willing to overrule earlier decisions that had upheld the restrictions.
Both justices spoke at length in their Senate confirmation hearings about the importance of abiding by precedents - even if they would have voted the other way had they been involved in an earlier decision.
On Wednesday, Alito questioned the basis for blocking corporate and union campaign donations.
More than half the states, including California, Washington and Virginia, allow corporations to make independent campaign expenditures.
"Have they all been overwhelmed by corruption?" Alito asked.
Justice Stephen Breyer expressed doubts about rolling back the requirements. He suggested that to do so might "make a hash" of campaign finance reforms enacted by Congress in 2002.
"Robust debate ... is the most fundamental value" protected by the First Amendment, argued Theodore Olson, the attorney representing Citizens United, the conservative group that made the movie. Olson said the government in this case "has prohibited speech."
Roberts seemed to suggest he's prepared to at least scale back restrictions.
"We don't trust our First Amendment rights to FEC bureaucrats," said the chief justice. The Federal Election Commission oversees the enforcement of campaign finance laws.
The justices were hearing arguments in the case for the second time. It began as a dispute over whether the Clinton movie should be regulated as a campaign ad.
But it took on greater significance after the justices decided to use the case to consider whether to ease restrictions on how corporations and labor unions may spend money to influence elections.
Besides Roberts and Alito, the other three conservative-leaning justices, Anthony Kennedy, Antonin Scalia and Clarence Thomas, are on record opposing the restrictions on corporations and unions. Restrictions on corporations have been around for more than 100 years; limits on unions date from the 1940s.
Citizens United wanted to air ads for the anti-Clinton movie and distribute it through video-on-demand services on local cable systems during the 2008 Democratic primary campaign.
But federal courts said the movie looked and sounded like a long campaign ad, and therefore should be regulated like one.
The movie was advertised on the Internet, sold on DVD and shown in a few theaters. Campaign regulations do not apply to DVDs, theaters or the Internet.
The film is filled with criticisms of the former first lady, whom President Barack Obama defeated in the primaries and then made his secretary of state. It includes Dick Morris, a former adviser to President Bill Clinton who is now a Clinton critic, saying the one-time candidate is "the closest thing we have in America to a European socialist."