In the ongoing federal government shutdown, one fiscal fact has raised some eyebrows. Despite the furlough of many federal employees, members of Congress are staying at work—with pay. One congressman, Rep. Mario Diaz-Balart (R-FL), answered a question about this from CNN’s Wolf Blitzer last week by noting, “There is a bit of a constitutional issue … when you are dealing with the paychecks of members of Congress.”

One generally shouldn’t trust politicians to know what they’re talking about when it comes to the Constitution, but the congressman got this one right. The reason is the 27th and latest constitutional amendment, which states: “No law, varying the compensation for the services of the Senators and Representatives, shall take effect, until an election of Representatives shall have intervened.”

The 27th Amendment was originally drafted and proposed in the late 1780s to address a criticism of the Congressional Compensation Clause in the Constitution’s Article I. This clause was ratified to ensure that members of Congress would be paid and thus less easily corrupted, and that they would be paid out of the federal treasury so that they wouldn’t be beholden to the states.

The Anti-Federalists protested, however, that the Compensation Clause gave members of Congress the unchecked power to vote themselves higher salaries as they pleased. To allay this fear, James Madison proposed the text of what would become the 27th Amendment as part of the original Bill of Rights—yet only six states ratified it at the time. Ohio’s legislature would ratify it during the “Salary Grab” scandal over retroactive congressional pay hikes in the 1870s, but then momentum stalled again.

In 1939, the U.S. Supreme Court ruled in the case of Coleman v. Miller that any proposed constitutional amendment submitted to the states without a ratification deadline can be ratified by the states at any time. This set the stage for a University of Texas college student named Gregory Watson who, in the process of writing a term paper, rediscovered the amendment in 1982 and organized a nationwide campaign to ratify it. His efforts came to fruition a decade later when Michigan became the 38th state to get on board, thus completing the Article V procedure for amending our Constitution.

So what does this late arrival to the constitutional party mean for the current shutdown shenanigans? Essentially, any changes to their own salaries that members of Congress vote themselves won’t kick in until those members face their constituents again at the ballot box. Note that the 27th Amendment refers to any law “varying” compensation, not just those increasing it. So even if Congress passed a law today to eliminate congressional salaries altogether, it wouldn’t take effect until the next Congress opens—in January 2015.

Since no government shutdown is likely to last that long, the 27th Amendment prevents Congress from cutting its own pay during one. Image-conscious legislators will simply have to pledge to refuse their paychecks, directing them to be held in indefinite escrow or donating them to charity.