You need to look up your state's recording consent laws, but generally any place where there is "no reasonable expectation of privacy" is considered legal to record audio, even in states that follow "two party consent" frameworks. Depending on the work place, it could be argued one way or the other and only a lawyer familiar with your state's laws could give a sure answer based on the specifics of your situation. A lot of states don't have any limitations on recording though so if you are in one of those you are obviously in the clear.