If you are receiving Maine Public Employees Retirement System (MainePERS) pension, going to work at a position not covered by MainePERS, there is no impact on your MainePERS pension.
If you are in receipt of Social Security retirement benefits, going to work may impact your Social Security retirement benefits.  The federal Social Security Administration has an “official age of retirement” based on your birth date.  If you receive Social Security retirement benefits prior to reaching your “official age of retirement” according to the Social Security Administration, your earnings can impact your Social Security retirement benefits.
The first step when deciding if you want to return to work, you need to ask the Social Security Administration your personal “official age of retirement.”  The Social Security Administration can provide you the amount you can earn before your Social Security retirement benefit is impacted.
Once you reach your “official age of retirement,” there is NO offset to your Social Security retirement benefit due to earnings.
If you return to public service covered by MainePERS, the state law has changed.  There was a state law that limited state retirees and educators’ wages and benefits if they returned to employment covered by MainePERS.   Those limitations have been removed.  The one limit is employment time after retirement will not be added to your MainePERS calculation for pension purposes.
https://www.mainepers.org/Retired%20Members/Retired_Return_to_Work.htm
https://www.investopedia.com/articles/personal-finance/120715/how-does-my-parttime-job-affect-social-security.asp
https://www.investopedia.com/ask/answers/020215/can-i-collect-social-security-if-i-still-have-job.asp