A federal appeals court in Boston heard arguments Wednesday about the constitutionality of a 2-year-old campaign finance law in Maine. The case deals with contributions to so-called super PACs, which now spend billions of dollars each year on elections nationwide to influence voters. Super PACs are political committees that make independent expenditures to support or oppose candidates. Since then, contributions to super PACs have exploded from $86 million to nearly $7 billion. Circuit Court of Appeals sides with Equal Citizens and upholds Maine’s law, the case would likely be reviewed by the Supreme Court.