Contact the police and fill out a police report they may also ask you to let the post office know and possibly speak to the postal police--and yes, there are postal police about your suspicions. Ask your employer to find out from their bank who cashed the check and where this may help confirm the identity of the perpetrator. Once you know who it is, you can sue that person as well as filing charges for the money. If it was a postal work, put in a claim for the money with the post office on the grounds it was their employee though they may not have to pay 1 employers are generally not responsible for their employees' criminal, as opposed to negligent/careless, acts and 2 the federal government has considerable immunity to lawsuits.The only way to get your money is from the thief and possibly his/her employer your own employer did its job by sending you the check and is not liable if someone unconnected with it stole it' they do not need to re-issue you a new check.