By Nick Assinder
Political correspondent, BBC News website
Gordon Brown has so far weathered three serious tests of his premiership - attempted bombings, floods and a foot-and-mouth outbreak. The prison officers' dispute has the potential to be more dangerous.
This is partly because, it is being argued, it is entirely of his own making as it was Mr Brown who, when chancellor, refused to meet the independently-recommended pay rise in full.
Prison officers have had their pay award staged
And partly it is because the row throws into sharp focus the problems of overcrowding, alleged under-funding and plunging morale in the country's jails.
Finally the risk is that it might strengthen the resolve of other public sector workers, most notably nurses in England who are also considering industrial action after he similarly staged their recommended rise.
The nurses will decide in a couple of weeks' time whether to accept a revised government's pay package after some 95% had voted to go ahead with a ballot on industrial action over the original pay award.
The way Mr Brown deals with the prison officers' dispute will be closely watched by those other workers and the opposition parties alike as they continue to assess just what sort of prime minister Gordon Brown intends to be.
It will also be a test of the prime minister's relationship with the wider union movement - still Labour's biggest donors - which has often seen him as more sympathetic towards them than his predecessor.
So far, the prime minister is adamant he will do nothing to undermine economic stability, which has led to union fears there will be no room for improvement in their pay offer.
Mr Straw has taken a hard line against strike
The Tories, meanwhile, lost no time in attacking Mr Brown over the dispute, claiming he refused cash for more prison places and warning the dispute could compromise security.
Inevitably, there will be talk of the possibility of a 1979-style winter of discontent when striking public sector workers effectively brought down the last Labour government under Jim Callaghan.
That is currently premature, but Mr Brown and ministers like Justice Secretary Jack Straw are painfully aware of the importance of the public sector workers to a Labour government.
Mr Straw acted immediately to win a court injunction against the strikers but the unions also won what they claimed were new talks with the government, with ministers clearly determined to halt this dispute before it escalates dangerously.
But there was even a row over whether that meeting had been planned before the strike or was a result of it.
The unions currently believe they can win public support for their action but that may be short lived, particularly if there is any suggestion safety is being compromised.
Any sign of a climb-down by the government may well strengthen the determination of other public sector workers to push their claims or take industrial action.
But too tough a line may well escalate the dispute and spark bitterness and resentment amongst other public sector workers and store up trouble for the future.
What the prime minister will certainly not want is a lengthy, escalating dispute to bring his political honeymoon to a swift end and recall bad memories of past clashes between Labour governments and the unions.