The Welsh Government's failure to win three votes in the assembly shows a government in crisis, Plaid Cymru AM Adam Price has claimed.
Illness, absence and mistakes meant that Labour AMs failed to stop a Tory vote attacking the state of Welsh roads from passing on Wednesday.
Mr Price said it was a "schoolboy error" that First Minister Carwyn Jones was not present.
A Welsh Government source derided the votes as "meaningless".
Opposition parties regularly hold debates in the assembly on Wednesday afternoons, where motions expressing opinions are tabled for votes.
Usually, the government's majority means that opposition motions - which are not binding on government policy - do not pass.
But on Wednesday three votes did not go the way the Welsh Government wanted them to.
Labour AM Dawn Bowden had been away ill, while First Minister Carwyn Jones and Economy Secretary Ken Skates were on government business.
The government had tried to stop a Conservative motion claiming that Wales' "substandard road infrastructure is costing the Welsh economy hundreds of millions of pounds a year" from passing.
An initial government attempt to get the motion effectively struck off failed by 26 votes to 27. The final vote on the matter went in the Tories' favour, 29 to 24, in part because two Labour AMs - Vikki Howells and Mick Antoniw - voted with the Tories, later telling BBC Wales they had done so by mistake.
The government also failed to get its way in another vote on a Plaid Cymru motion about homelessness, with 26 AMs on the government's side and 27 in opposition, although Plaid's form of words ultimately did not clear the assembly.
"I think it does raise serious question marks about Labour's business management, and the whipping system," said Mr Price, referring to measures ensuring AMs vote as their party tells them to.
He said there were "serious question marks" around the Labour chief whip Julie James - who took over from Jane Hutt in last November's government reshuffle.
"You only need a combination of factors and even with the notional majority that bringing Dafydd Elis Thomas into the government may have provided, it's wafer thin.
"And if your party management isn't up to scratch then you're going to get yourself into difficulties."
Plaid Cymru is also no longer helping the government by "pairing" members - who will decline to vote to compensate for absent Labour AMs - since it scrapped the so-called "compact" co-operation agreement.
"It does connect with a wider sense of a government that is in a state of disarray at the moment," Mr Price said, referring to events following the death of sacked cabinet secretary Carl Sargeant.
"There's been all the issues before Christmas that we're well aware of which are continuing, and will certainly dominate the political agenda for the next several months, [and] a continuing question mark over Carwyn Jones's future as first minister.
"One imagines that it is very difficult for people to keep their eye on the ball and just to do the basics in a focused and disciplined manner.
"I think the fact that this series of votes was lost was indicative of this wider crisis.
"The government losing a vote because the first minister couldn't be present - that is a schoolgirl, schoolboy error that should never have been allowed."
Welsh Conservative leader Andrew RT Davies said: "It's proof that there is an alternative to Labour when opposition parties work together to highlight and expose their failings."
A Welsh Government source said: "Opposition day votes are - in many ways - meaningless.
"They aren't binding and don't have any bearing on government policy or delivery."
Asked about Labour AMs apparently voting with the opposition by mistake, a spokesman for the Labour group in the assembly said: "We don't comment on whipping matters."