AMs are not meant to use assembly facilities for party-political campaigning.
But in March, South Wales Central AM Neil McEvoy discussed the campaign at a press conference held in an assembly briefing room.
Mr McEvoy accepted that he was in breach of the AM's code of conduct.
The standards committee has recommended to the assembly that Mr McEvoy be censured for the breach - a formal reprimand.
Their conclusion follows an investigation by the standards commissioner Sir Roderick Evans who said Mr McEvoy "failed to comply" with the rules on 14 March.
The press conference was held while Mr McEvoy was suspended from his party group in March - a suspension that was later lifted.
In a statement, Mr McEvoy said he distributed copies of a document at the press conference which contained seven policies relevant to the local elections, saying they were relevant to his suspension.
He said: "This was not appropriate. I accept that it was in breach of the code of conduct."
A Plaid Cymru spokeswoman said: "This is a matter for the individual member who apologised and we are pleased that this matter has been resolved."
A Plaid Cymru AM has apologised for discussing his party's council election campaign at a press conference in the Senedd building.