This month, the U.S. Supreme Court is threatening to strike down key provisions of the 2002 “McCain-Feingold” bipartisan campaign finance reform act, overruling two of its prior rulings in the process and uprooting a century-old principle – existent in American law since Teddy Roosevelt’s Administration – that corporations should be barred from making unlimited expenditures in elections.

Wait, what? What did I just say? Corporations might soon be able to make unlimited expenditures in elections? Can they do that?

The answer is yes, if the Supreme Court says they can. And if you didn’t know that already, you should certainly keep reading.

The case I’m referring to, of course, is Citizens United v. Federal Election Commission, which is being argued before the Court, for the second time, tomorrow morning. The reason the Court is hearing this case again is because in June, the Court ordered that the scope of the case be dramatically expanded following its first oral argument in March. At that time, Citizens United, a conservative non-profit corporation, was focused upon the FEC’s decision to treat “Hillary: The Movie” – its feature-length film criticizing Hillary Clinton during last year’s Democratic primaries – as a standard attack ad for the purposes of campaign spending regulations. Citizens United, which is subject to campaign regulation because it accepts money from businesses, argued that the film did not constitute an “electioneering communication” as defined by federal law. Not surprisingly, the FEC disagreed.

However, once the Court decided to hear the case, Citizens United – represented by Bush Solicitor General Ted Olsen — began to push for massive changes in settled campaign finance law, arguing that corporations’ “speech” (i.e., their expenditures) in elections was entitled to just as much protection under the First Amendment as speech by individuals. This argument has been raised many times by conservatives and business leaders throughout the years, and rejected repeatedly by the Court. (While current federal law allows business corporations to form political action committees, or PACs, with money collected from individuals associated with the corporation, it clearly prohibits them from using money from their general treasuries — where all their profits sit – to influence elections.) Nevertheless, to the horror of the members of Congress and progressive groups who worked so hard to pass campaign finance reform, the conservative justices on the Roberts Court seemed amenable to the argument that restrictions on corporate spending on elections were unconstitutional. Rather than deciding the case last June, the Court asked the parties to supply supplemental briefing on the constitutional question, scheduling a special September session to re-hear argument.

What the Court threatens to do now is remove these restrictions, and say that corporations can funnel unlimited amounts of money from their corporate treasuries into elections. Citizens United argues that because individuals can spend unlimited amounts of money to influence elections, corporations should be able to do so as well, in essence asserting that there is no difference between corporations and individuals when it comes to spending money on elections.

That this is an absurd assertion should be obvious to everyone, but especially to progressives, who have been fighting corporate “voices” for generations. If the Court accepts this argument, it will be undoing over 100 years of progress in campaign finance rules, starting with the Tillman Act of 1907, which established that corporations are distinct from individuals and must not be able to spend their profits in elections. This distinction builds on the text of our Constitution, which never mentions corporations, and on two hundred years of Supreme Court rulings that treat corporations and individuals differently. Abolishing this distinction will release the floodgates of corporate money – in quantities that are orders of magnitude greater than what is spent now – into federal and state elections. It will, in one fell swoop, undo decades of hard work by progressives who have fought to adopt strong campaign finance and disclosure laws. And perhaps most urgently, such a ruling stands to undo the benefits of the months of exhausting work done by millions of progressives to elect Barack Obama and progressive leaders in Congress, undermining or placing out of reach nearly every outcome on the progressive agenda, from health care reform, to clean energy, Net neutrality, consumer protection, civil rights, and more.

Think for a second about how you would have reacted to a proposal sponsored by the Bush Administration in 2003 to repeal a century’s worth of campaign finance laws that limit the ability of corporations to influence elections. Constructively engaging and pushing back against the conservative activism of the Roberts Court is trickier, but no less important. At the very least, we should all be expressing our outrage. The justices on the Supreme Court do keep an ear toward public opinion, and it is too often because progressives at large are silent about the issues and cases that come before them that they’re able to quietly, though tragically, chip away at our work. We owe it to ourselves not to let that happen here. We need to make noise about this case, and we need to do it now.

Hannah McCrea is proud to work for the Constitutional Accountability Center (CAC), a law firm and think tank dedicated to demonstrating how the text and history of the Constitution uphold progressive outcomes.