In perhaps the biggest challenge yet to the school rankings industry, both Yale and Harvard announced Wednesday that they were withdrawing from the influential U.S. News & World Report rankings of the nation’s best law schools.

Colleges and universities have been critical of the U.S. News ranking system for decades, saying that it was unreliable and skewed educational priorities, but they had rarely taken action to thwart it, and every year almost always submitted their data for judgment on their various undergraduate and graduate programs.

Now both Yale and Harvard law schools have announced that they will no longer cooperate. In two separate letters posted on their websites, the law school deans excoriated U.S. News for using a methodology that they said devalued the efforts of schools like their own to recruit poor and working-class students, provide financial aid based on need and encourage students to go into low-paid public service law after graduation.

“It has become impossible to reconcile our principles and commitments with the methodology and incentives the U.S. News rankings reflect,” John F. Manning, the dean of Harvard Law, said in his statement.