Economists have greatly criticized regulations that impose uniform env
ironmental standards. Such a critic ignores that the implementation of
the standards may vary significantly across plants, thus giving rise
in fact to non-uniform standards. The purpose of this paper is to anal
yze the determinants of the regulator's monitoring activities. We show
that greater inspection effort, ceteris paribus, is allocated towards
those plants whose emissions are likely to generate a higher level of
damages. On the other hand, we show that the behavior of the regulato
r is also a function of variables that may not be directly related to
abatement cost and damages. In particular, we show that variables pert
aining to local labor market conditions have an impact on the monitori
ng strategy adopted by the regulator.