The standard seems to be that Congress must only use "prophylactic" measures to enforce the 14th amendment. You know the Boerne "congruent and proportional" standard.
We only looked at this within the context of the 11th amendment ban on lawsuits against states. A lot of discussion of this was in the 11th amendment cases in the 90s, when the court tried to flesh out the Boerne standard and say what was valid under Article 5 and what wasn't.
-Kimel v. Florida Board of Regents, 2000 (concerning whether provisions of the Age Discrimination in Employment Act are valid pursuant to the 14th)
-Board of Trustees of the Univ. of Alabama v. Garrett, 2001 (Americans with Disabilities Act)
-Tennessee v. Lane, 2004 (ADA again)