The leader of the Conservative opposition was given a slap on the wrists after a committee found his "false" social media posts brought the Senedd into disrepute.
Andrew RT Davies was formally reprimanded by fellow Senedd members following an investigation into a tweet describing 20mph as a "blanket" policy.
Douglas Bain, the standards commissioner, concluded Mr Davies breached the code of conduct by continuing to use the term despite a ruling it was "imprecise and inaccurate".
The Tory was found to have brought the Senedd into disrepute but cleared of breaking rules on honesty, with Mr Bain saying: "I am satisfied it was not his intention to deceive anyone."
In his report, Mr Bain wrote: "When he posted the tweet the member knew – or ought to have known that – although it was not untruthful or dishonest, it was false."
'Misleading'
The South Wales Central MS, who has led the Tory group in two stints since 2011, did not attend the debating chamber or Siambr on Wednesday as his peers agreed to censure him.
Hannah Blythyn, who chairs the standards committee, raised concerns about a steady increase in complaints about Senedd members' conduct on social media.
She said: "I would like to take this opportunity to remind members: while we recognise that social media is a tool that has the potential to be used effectively for communication and debate, it is for members to determine the accuracy of information they are posting."
Senedd members backed the motion to endorse the committee's recommendation with no objection from the Conservative benches, doing away with the need for a vote.
Mr Davies was also found to have breached rules following a separate complaint about a "misleading and dangerous" tweet but the Senedd agreed to take no further action on this.
'Contempt'
Labour's Lee Waters, who introduced the default 20mph policy, expected better from a Senedd member, "let alone the leader of the opposition in our national parliament".
He said: "A censure by this Senedd is a solemn thing, none of us should take lightly a rebuke by our peers or a finding against us by the independent standards commissioner."
"But I'm bound to note a pattern of behaviour by the leader of the opposition...and the fact he's not here this afternoon...."
"I'm not aware if he's offered any explanation but it speaks of a contempt about our standards. This is not the first time his words and conduct have been questioned."
Mr Waters added: "Describing the change in speed limit as a blanket one, when it only applies to a minority of roads, is clearly deliberate and intended to mislead. But this isn't some jolly jape, lives are at stake, and confusion is sowed by inaccurate use of language."
'Desperate'
In September, Natasha Asghar, the Tory shadow transport secretary, was similarly given a ticking off by the Senedd for depicting 20mph as a "blanket" policy.
She refused to back down, saying: "To say that I brought the Senedd into disrepute by using the word 'blanket' is purely absurd."
"I make no apology whatsoever for standing up for my constituents and residents across Wales when it comes to the Welsh Government's 20mph scheme."
The complaint against her was submitted by Mr Waters and Ms Asghar vowed to continue campaigning despite "desperate" attempts to stop her.
Mr Bain accused Ms Asghar of "saying one thing and doing the opposite", writing: "I have no doubt that such conduct is unacceptable and...brings the Senedd into disrepute."
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