The Constitution’s Compact Clause provides that “No State shall, without the Consent of Congress…enter into any Agreement or Compact with another State.”[18] The Founders created the Compact Clause because they feared that compacting states would threaten the supremacy of the federal government in matters of foreign affairs and relations among the states.[19] If states could make agreements among themselves, they could damage the nation’s federalist structure. Populist states, for example, cannot agree to have their U.S. Senators vote to seat only one Senator from a less populous state...
But that's not because of the compacts clause.
THat's because Article V says "no State shall be deprived of equal suffrage in the Senate without its consent".