See primarily Thirty-thousand.org (after the Constitutionally minimum size of a Congressional district)
These in turn seem to be spurred on by a Boston Globe article:
Divide Iraq’s 25 million people by the number of members in the new parliament (275), and the result is one legislator for every 91,000 people. That will make Iraq’s government almost exactly as representative as Great Britain’s — each member of the House of Commons also represents, on average, about 91,000 citizens. Other democracies are comparable. The ratio for Italy’s Chamber of Deputies is 1 to 92,000. For the French National Assembly, 1 to 104,000. For Canada’s House of Commons, 1 to 105,000. For Germany’s Bundestag, 1 to 136,000.
But in the US House of Representatives, each lawmaker represents, on average, a staggering 674,000 citizens. That makes the “people’s house” in Washington one of the least democratic bodies of its kind in the world.
Whatever the impetus, this is a heck of a good idea, and one which does not require a change to the Constitution.