Article I, Section 10, Clause 3: "No State shall, without the Consent of Congress, ...enter into any Agreement or Compact with another State..."
You might want to actually try reading the Constitution sometime. There are no pictures, but I'll be glad to help you with all the big words.
And if YOU read the article above, you might note that these states ARE entering into a compact, and Congress isn't involved. Oh, no, it's unConstitutional! So is the notion of excluding jury rights in suits at common law where the value in controversy is over twenty dollars, but then, you'd never know that from the U.S. Supreme Court, either. Thank goodness we have you around to kiss their 'interpreting-a-living-document-might-makes-right' fannies.