Tessa Jowell, Secretary of State for Culture, is leading a revolt against the so-called "smoking carriage" compromise ahead of a meeting tomorrow.
She has written to campaigners setting out her opposition to the loophole proposed by Patricia Hewitt, Secretary of State for Health.
David Blunkett and David Miliband are also determined to block Ms Hewitt when senior ministers discuss the proposed legislation at noon on Monday.
The increasingly rancorous cabinet split threatens to spill into the public arena with the imminent release of Ms Jowell's letter to the campaign group Action on Smoking and Health, setting out her opposition to the policy.
Its publication will be the worst breakdown in cabinet discipline since Mr Blunkett delivered a blunt assessment of his colleagues to his biographer.
A senior official at the Department of Health insisted that Ms Hewitt would succeed in driving through the compromise in time for the unveiling of the Health Improvement Bill on Wednesday.
"Her colleagues will have to abide by the decision that is taken," said the official.
Ms Hewitt drew up the "smoking carriage" plans when it became clear that an earlier compromise would be unenforceable.
Originally ministers had suggested that smoking be allowed in bars that did not serve food, but that policy has been dropped over fears that it would be impossible to protect bar staff from the effects of passive smoking.
Tony Blair is thought to have given the compromise his blessing and it is being backed by John Reid, the previous health secretary, who first sought to water down a full ban.