AMs that complain about other assembly members to a standards watchdog have been warned from making it public.
Standards Commissioner Sir Roderick Evans said the Labour Environment Minister Hannah Blythyn should not have publicised her complaint about UKIP AM Michelle Brown's use of a racial slur.
Sir Roderick said publicity would be seen as "strong evidence" of a breach of the AMs' code of conduct.
Ms Brown was excluded from the assembly for a week. Labour declined to comment.
The UKIP AM for North Wales faced action after she was investigated over a private phone call where she used a racial slur to describe Labour MP Chuka Umunna.
Sir Roderick said the complaints procedure was meant to be dealt with confidentially to protect AMs "against adverse publicity from a complaint which ultimately may be found to be without merit".
Ms Blythyn - who made the complaint in her former role as chair of the Labour group - told Sir Roderick that the letter was released "in the interests of full transparency", according to a subsequent letter written by the commissioner which BBC Wales has seen.
But the commissioner said he could not justify a unilateral decision to "deviate from the confidentiality required by the procedure set down by the Assembly".
Sir Roderick said publicity of a complaint could also arise suspicions "rightly or wrongly" that the assembly complaints procedure is being used to make a political point or to gain a political advantage.
"Such suspicions undermine the integrity of the Assembly's processes and I will jealously guard against the danger of my office being used in that way," he said.
The commissioner said that because the complaint was on behalf of a political group, parties should be aware that it means the committee member of the party concerned cannot then sit on standards committee when it considers the complaint.
In the case of Ms Brown, the standards committee had to sit without its Labour chairwoman, Jayne Bryant, while it considered her case.
The committee went on to recommend Ms Brown's exclusion for a week.