They want to cap "combined employee/employer pre-tax contributions to 401(k)s at $20,000 or 20 percent of income, whichever is lower. That would be a substantial cut in deductibility, since the employee deduction alone currently is capped at $16,500 (savers over age 50 can make additional $5,500 “catch-up” contributions)."
Just one of the ways the greedy feds want to extract more revenue from people as they age.
You'll find more of this discussed, here.