A 24-hour strike by London Underground workers is to go ahead from Wednesday evening in a bitter row over plans for all-night Tubes, threatening a fresh bout of travel chaos for commuters and tourists.
The drivers' union Aslef accused LU of being "completely inflexible" over terms and conditions for the service, leaving it with "no other choice" than to press ahead with the walkout.
The union said the company should postpone the planned launch of the service on September 12 so that further negotiations could be held.
Aslef officer Finn Brennan said: "This leaves us with no other choice than to go ahead with strike action from 9.30pm on Wednesday.
"We genuinely regret the disruption this will cause, but the blame for this must rest with the pig-headed determination of the mayor to insist on a September 12 launch of night Tube instead of allowing more time for a negotiated settlement to be reached."
Other union members are due to strike from 6.30pm, meaning that disruption will start late in the afternoon as workers try to get home to beat the action.
Transport for London said Tube services will stop running at 6.30pm on Wednesday, and urged people to complete journeys by this time and travel earlier if possible.
Tube services are expected to be "exceptionally busy" between 4.30pm and 6.30pm.
Staff on the bus network, DLR, London Overground, tram and TfL Rail services will not be on strike, but these services are expected to be much busier than usual.
There will be no Tube services all day on Thursday. Extra bus and river services will run, and all other public transport services and roads will be much busier than usual.
Aslef said the overwhelming view of its members was that the latest offer was unacceptable.
Mr Brennan said: "The main concern is the complete lack of firm commitments on work life balance for train drivers. Our members want guarantees on the number of weekend rest days they will have under both the interim and long term arrangements for night Tube. Vague phrases like "will seek to mitigate" and "will explore" are simply unconvincing.
"We would be prepared to continue discussions to try to find common ground, but senior management are insistent that new rosters will be issued this week so that night Tube starts on September 12."
The RMT said it had also rejected the "re-packaged" offer, saying its reps were "furious" when they examined details of the proposed deal.
A statement said: "They are a re-hash of previous plans and would continue along the course of smashing up long-standing agreements and destroying work/life balance in the interests of delivering the mayor's ill-conceived night Tube vanity project.
"RMT will now be embarking on a renewed campaign to inform the public of the heavy price that the millions of weekday commuters, paying thousands of pounds of year, will be paying in terms of safety, reliability and quality in order to get a few thousand revellers home from central London in the early hours of Saturday and Sunday morning."
The RMT questioned the viability of getting the new services running on September 12 "without any adequate risk assessments, a complete ignorance of the consequence of losing the weekend engineering and maintenance slots and without any agreement in place on staffing arrangements".
General secretary Mick Cash said: "Our members have made it clear that the latest offer from London Underground is merely a rehash of the previous package and does nothing to tackle the core issue which revolves around staff being at the beck and call of management to be hauled in during their free time to try and plug the staffing gaps which riddle the mayor's night Tube vanity project.
"RMT is also deeply concerned that the talks are being conducted by people who have no background on the Tube and no understanding of how processes and logistics work.
"That is a major barrier to progress in the talks and one that we hope can now be cleared.
"The night Tube plan has been botched from the off. The basics haven't been done and those who will pay for this shambles will not only be our members but the London daily travelling public who cough up a fortune and who will find their safety and the reliability of the service compromised from September 12 onwards."
Manuel Cortes, leader of the TSSA rail union, said: "The night Tube was a gimmick when Boris Johnson announced it and it remains a gimmick today.
"The only difference is that he has now worked out that he may not be able to afford it after all. Our private information is that it will not break even until 2033.
"This is the reason he is now gambling with the health and safety of our members. Now he wants to blame the unions for failing to start it on time next month.
"This is not about industrial relations, it is about politics and Boris's long term drive towards Downing Street."
LU said the unions were continuing to demand more money, the hiring of more staff - including for ticket offices that customers no longer use - and further guarantees on what they consider to be issues around work-life balance, including a 32 hour, four day week.
Chief operating officer Steve Griffiths, said: "After listening to the unions, we put forward an extremely fair revised offer, which addresses their concerns over work life balance and rewards our people for the hard work they do in keeping London working and growing.
"Despite this, the new offer has been rejected outright by the union leadership, again without consulting their members. We continue to urge them to put the new offer to their members and not subject Londoners to further unnecessary disruption. We remain available for talks at any time."
LU's managing director Nick Brown said he was "hugely disappointed" that the unions had rejected the latest "very fair" offer.
He told the Press Association that the offer should be put to union members for a vote because it promised a good pay rise and assurance on work/life balance.
He insisted rosters for September 12 were "ready to go", adding that the offer remained on the table.
"The unions' reasons for rejection are pretty thin," he added.
The changed offer included an extra £200 per night Tube shift for drivers while the new service is introduced and a £500 bonus for station staff by next February.
After a short transition period while the service is introduced, drivers will have the choice whether to work nights, said LU, and everyone will be entitled to two days off in seven.
Unite official Hugh Roberts said: "We have engaged in Acas talks in a positive manner hopeful that we could avoid further industrial action. Sadly, that has not been the case with London Underground which has rehashed previous offers and failed to give future guarantees over work/life balance and unsocial hours working."