Congressional Apportionment Amendment - Wikipedia
But it's a real amendment, it was passed by Congress in 1789 as part of the Bill of Rights, it has 11 valid ratifications, and it would become part of the Constitution with 27 more ratifications, the same way the 27th amendment did in 1992.
David A. Johnston
This was actually considered in the US Constitional amendments as the first proposed amendment. It’s a shame it hasn’t been ratified. YET.