All 113 London fire stations are joining the national strike later in a dispute over changes to pension schemes.
The 5500 firefighters across the capital will go on strike between 7pm and midnight.
The London Fire Brigade say a contingency plan is in place.
The Government will hear this week if it faces the threat of the first national firefighters' strike for a decade, in a row over pensions.
Members of the Fire Brigades Union have been voting on whether to launch a campaign of industrial action, with the result due at the end of the week.
The union said planned changes were "unaffordable and unworkable", would impose an increase in members' contributions and would put firefighters at greater risk of dismissal without access to a proper pension if they cannot maintain fitness standards as they approach the retirement age of 60.
A union leader has confirmed he is in talks with counterparts about staging a general strike.
Mark Serwotka, general secretary of the Public and Commercial Services Union (PCS), said discussions were under way about action that would show people can "fight back".
It comes after it emerged last week that Unite had submitted documents to the TUC calling for a 24-hour general strike against austerity measures.
Ambulance drivers will go on strike today in a bitter row over cuts and union recognition.
Staff and paramedics will mount picket lines outside ambulance stations across the county.
Unite said its 450 members at the Yorkshire Ambulance Service NHS Trust will walk out for 24 hours after the failure to break the deadlock.
Members of other unions are not involved in the action and will be working normally to provide emergency cover and other services.
Unite said it was de-recognised after raising concerns about patient safety over plans to make savings of £46 million over the next five years.
The union said there were proposals to employ emergency care assistants, with only a few weeks training, alongside paramedics.
The head of the NASUWT teachers' union, Chris Keates, has accused the Education Secretary Michael Gove of “recklessly pursued a relentless attack on the profession".
He called on Mr Gove to respond to the union's "reasonable demands" in order to avoid "widespread disruption in schools" this summer.
NUT head Christine Blower warned that the pensions situation and increased workload is "making teaching an unsustainable option for many".
The two largest teaching unions, NUT and NASUWT, have announced a series of industrial actions in response to their dispute with the government over pay, pensions and workload.
The actions include:
- National rallies across England and Wales in April and May
- National strikes starting in the North West on June 27
If the Education Secretary does not "respond positively to the unions’ demands" there is also a chance of further strike action in the Autumn term, including a one-day nationwide strike.
Teachers in England are to stage a series of strikes in the summer, the National Union of Teachers and the NASUWT announced today.
The strikes are part of a continuing row over pay, pensions and workload.
At a time when the private sector is working extremely hard to get the economy back into growth, it is extremely frustrating to see public sector unions going out on strike.
Civil servants already enjoy better pay and pensions than the wider workforce, but Mark Serwotka thinks they should take no share of the pain involved in sorting out the public finances.
It sends an awful message to investors around the world for the PCS to strike on Budget Day in an attempt to prevent the essential work of reducing the deficit.
The Government said it will address some of its terms and conditions for employees after public sector workers called a strike:
While there has been significant recent change in pay and pensions, there are other terms and conditions that have not been updated.
We will address this and ensure a modern employment offer is available to all.
The Government said "pay restraint" had helped protect jobs and its pensions remain "among the very best available" after civil servants announced a strike:
The Government took the tough decision to freeze public sector pay for two years, while protecting those earning under £21,000 by increasing their pay by at least £250 per year.
Pay restraint has helped to protect jobs in the public sector and support high- quality public services.
In March 2012 we set out our final proposed agreements on pension reform following more than a year of intensive discussions with trade unions.
These reforms will ensure that public sector pensions will remain among the very best available and that they can be sustained for future generations.