14. It is that section that requires pre-clearance.
But it just covers changes in voter procedures (picture i.d for example) but it doesn't cover gerrymandering. Usually any gerrymandering challenge goes directly to the federal courts. The Supreme Court over the years (both liberal and conservative courts) has made it very tough to challenge gerrymandering. Usually it is only successful when the gerrymandering is done strictly on racial grounds. That is usually not the case.