Rep. Ed Markey (D-Mass.), the frontrunner to become the next senator from Massachusetts, this week compared the Citizens United Supreme Court case to the Dred Scott decision that upheld slavery.

"The constitution must be amended," Markey says in a video posted to YouTube by a user named Bob Cleary. "The Dred Scott decision had to be repealed; we have to repeal Citizens United."

According to the video, the remarks came at an event Tuesday in Pittsfield, Mass. The news was first reported by BuzzFeed.

Democrats have routinely spoken out against Citizens United, a landmark Supreme Court case that paved the way for unlimited donations to so-called super PACs.

And Massachusetts has been perhaps the most anti-Citizens United state, with both candidates in its 2012 Senate race agreeing to a deal that prevented third-party groups from advertising on their behalf. Markey and his Democratic primary opponent, Rep. Stephen Lynch, have agreed to a similar arrangement in the special election for Secretary of State John Kerry's (D-Mass.) old Senate seat.

This is not the first time Citizens United has been mentioned in the same breath as Dred Scott. Republican former congressman Jim Leach (Iowa), in an October Boston Globe op-ed, said the reasoning behind the two cases is similar -- a much more direct comparison.

"Brazenly, in Citizens United, the court employed parallel logic to the syllogism embedded in the most repugnant ruling it ever made, the 1857 Dred Scott decision," Leach wrote. "To justify slavery, the court in Dred Scott defined a class of human beings as private property. To magnify corporate power a century and a half later, it defined a class of private property (corporations) as people."

Update 10:48 a.m.: Markey's campaign has released the following statement from the congressman: "Citizens United is poisoning the democratic process in America and that is completely wrong. Karl Rove, the Koch Brothers and anonymous special interests have no place in our elections and no place in this Senate race. I repeat my challenge to all Republican candidates to accept the people's pledge to keep this toxic outside spending and negative advertising out of the Senate race."

National Republican Senatorial Committee spokesman Brad Dayspring, meanwhile, offers this: "Agree or disagree with federal campaign finance law, it's ridiculous and offensive to compare it to the horror of slavery. Out-of-touch statements like these simply reinforce the fact that Ed Markey has been hibernating in Washington back rooms since Carlton Fisk was behind the plate for the Red Sox and disco ruled the world."