A person posing as a Therapeutic Goods Administration official has walked into a Melbourne health clinic and demanded vaccination posters be removed.

The Commonwealth organisation says it is aware of the impersonation and warned anyone else thinking of trying the trick would be breaking the law.

"Impersonating Commonwealth public officials is a criminal offence," the Therapeutic Goods Administration said in a statement on Thursday.

"We advise individuals who may be encouraged to impersonate an officer of the TGA that this is a serious criminal offence that may lead to prosecution."