Strikes across Tube and Metro networks in London and Paris have caused frustration for travellers on Thursday.
Workers in the two European capitals have walked out over concerns about jobs, pensions and pay.
Travel was widely disrupted throughout London’s tube network on both Thursday and Friday morning. Commuters have been urged to avoid travel on the network.
Nine out of 11 London Underground lines were shut on Thursday morning, according to Transport for London's (TfL) website.
The Central and Northern lines were partially open, with trains running on a small section of their normal routes.
The London Overground and Docklands Light Railway (DLR) were also suspended.
In Paris, travel will be interrupted on five metro lines out of 16, according to the latest update on the website of transport operator RATP, which advised people to work from home if possible. Significant disruptions are also expected on most of the other lines, RER commuter trains and buses.
Thursday’s stoppage is the latest of a series of protests pushing for higher wages.
In France, strikes by oil refinery workers disrupted fuel distribution last month, causing shortages at filling stations across the country.
Thousands of people joined demonstrations in Paris on October 18 to demand a bigger share of corporate profits.
In London, TfL is under pressure to cut costs following a funding agreement with the national government that leaves it with a budget deficit.
The agreement requires it to develop options around pensions, but TfL said if changes are to be made, there will be consultations and further work before any decisions are taken.
The Rail, Maritime and Transport (RMT) union said it has asked TfL to pause any job cuts and pension changes to give both sides time to negotiate a deal.
Assistant general secretary John Leach called on transport bosses to "stand by" their staff.
He told the PA news agency outside King's Cross St Pancras station: "My message to TfL now is stand by your staff, listen to your staff, thousands of them are on strike today for the sixth time this year.
"They're losing lots of money, don't they realise in management there's a serious problem here? What they need to do is stand with their staff.
"The Mayor of London needs to stand up for staff and do a proper finance deal which gives TfL money it needs to keep the capital city moving, and not trade off the staff pension, jobs and their conditions of employment for some bad deal, which is what they have done."
Londoners, and the wider UK public, have suffered months of strikes as workers fight for pay rises that keep up with inflation.
The action comes a day after the Royal College of Nursing announced British nurses had voted to strike, their first UK-wide walkout in the union's 106-year history.
That has followed walk outs by everyone from UK barristers to postmen and rubbish collectors in recent months over disputes about pay, jobs, pensions and conditions.
A planned strike by staff on overground trains this week was called off as negotiations continue.
Picket lines were formed outside Tube stations across the capital on Thursday morning.
The RMT said it had offered to suspend the strike during talks, but accused TfL of rejecting its proposals.
TfL's chief operating officer, Glynn Barton, said no proposals to change pensions or conditions have been made.
TfL's recent funding agreement with the government requires it to develop options around pensions, but the organisation said if changes are to be made, there will be consultations and further work before any decisions are taken.
The RMT said it has asked TfL to pause any job cuts and pension changes to give both sides time to negotiate a deal.
General secretary Mick Lynch said: “TfL have missed a golden opportunity to make progress in these negotiations and avoid strike action.
“Our members are resolute in their determination to see a just settlement to this dispute, and they will continue their industrial campaign for as long as it takes.”
More than 1,000 Unite members are on strike.
Unite's general secretary, Sharon Graham, said: “TfL is needlessly attacking our members' pay and pensions, which Unite simply can't accept. The workers have the full support of their union in fighting these attacks.
“TfL must stop behaving like a race-to-the-bottom employer and put forward an offer that is acceptable to our members.”
Unite regional officer Simon McCartney said there was no need for TfL to press ahead with “these attacks”.
“The pension scheme is financially viable and in credit and the savings TfL were forced to make have already been found elsewhere. It is high time London's Labour mayor, Sadiq Khan, intervened.”
Conservative councillor Dan Friend criticised Mr Khan on Twitter, blaming him for the travel “chaos”.
He tweeted: “Tubes are empty today as millions of Londoners suffer yet another day of strikes thanks to Sadiq Khan and Labour.
“They're backing the unions causing this chaos.”
