Locality Pay Equity Act of 2018 This bill: (1) prohibits the Office of Personnel Management (OPM) from defining more than one local wage area for prevailing rate employees within a pay locality, except with respect to the pay locality designated as "Rest of United States"; and (2) requires the OPM to ensure that this bill shall not have the effect of reducing any rate of basic pay for any individual who is serving as a prevailing rate employee.