"Otherwise every desirable place to live will be destroyed by overpopulation."  There are only three ways to prevent overpopulation; Limit breeding, kill the excess population; or prohibit movement into an "area, county, state, etc., or dies".

Killing them and internal passports and movement restrictions are illegal, but sterilization by eugenics was still approved in Oregon in 1972 by the Oregon Court of Appeals so I went with the legal method left.