Strike action over labour law reforms gripped France on Thursday, with oil refineries, nuclear power stations and transport hubs disrupted.
Riot police battled protesters in Paris and other cities, making 77 arrests, while 15 officers were injured and cars and shops were vandalised.
Prime Minister Manuel Valls insists the reforms will not be withdrawn but has suggested they could be "modified".
France is due to host the Euro 2016 football championships next month.
A state of emergency imposed after November's deadly attack by militants from the so-called Islamic State group in Paris remains in place.
The CGT union is leading the action, supported by six other unions including Force Ouvriere and Unef, whereas the more moderate CFDT union backs the labour reforms.
Tear gas filled the air as police in Paris struggled to contain a march which set off from Place de la Bastille.
Of the arrests, 36 were made in the capital while other cities like Lyon and Bordeaux saw similar confrontations.
Officials say 153,000 people took part across France though union leaders put the number at nearly twice that.
French labour reform bill - main points
- The 35-hour week remains in place, but as an average. Firms can negotiate with local trade unions on more or fewer hours from week to week, up to a maximum of 46 hours
- Firms are given greater freedom to reduce pay
- The law eases conditions for laying off workers, strongly regulated in France. It is hoped companies will take on more people if they know they can shed jobs in case of a downturn
- Employers given more leeway to negotiate holidays and special leave, such as maternity or for getting married. These are currently also heavily regulated
Flights to and from Paris, Nantes and Toulouse were affected, and a rolling strike by train drivers brought further disruption to regional and commuter rail services.
RTE, the body overseeing France's national power network, said stoppages at nuclear power stations were not having an immediate effect on electricity supply but warned, "If it worsens, it will have an impact on the management of the network."
A third of petrol stations were dry or dangerously low on fuel after days of blockades at refineries by union activists.
Five of the country's eight refineries remained at standstill or were operating at reduced capacity on Thursday.
'Not such a bad thing'
Mr Valls indicated there might "still be changes, improvements" made to the labour reform laws.
But he rejected Finance Minister Michel Sapin's suggestion that Article 2 of the bill could be rewritten.
Article 2 gives individual companies the power to opt out of national obligations on labour protection if they feel they need to - something the CGT union fiercely opposes.
German Finance Minister Wolfgang Schaeuble backed the reform, saying: "France can live with such disputes."
"A certain dissatisfaction of voters with their respective rulers isn't such a bad thing in principle," he added.
Unions were enraged by the government's decision to use a constitutional device to allow its watered-down labour reforms to be made into law without parliamentary approval.
The government says the reforms, which make it easier for companies to hire and fire staff, are needed to bring down unemployment.
The CGT has called for another day of action on 14 June, four days after Euro 2016 opens.
"The government has the time to say 'let's stop the clock' and everything will be OK," CGT chief Philippe Martinez told Reuters news agency when asked if his union was willing to disrupt the tournament.