Sud-Rail union announced on Tuesday, after a national council meeting, that it was calling on its members to walk off the job on July 6 and 7, the first weekend of the school summer holidays.
The hardline CGT, which is the most influential union among rail workers, had last week also proposed extending the rolling rail strikes on Friday 6th and Saturday July 7th, the first weekend of the grandes vacances, when many French head off on holiday.
But the CFDT-Cheminots, another major union for workers in the state-run SNCF rail company, decided on Tuesday not to take part in any strikes over the summer.
It said it would keep its powder dry until September, when unions will engage with SNCF management to try and agree the terms for workers under the reform of the debt-laden state rail operator.
UNSA, another big union in the SNCF, has already said it will not take part in any strikes in July.
With only two unions out of four opting to continue their strike on the first weekend of the summer holidays, it is not clear what the disruption will be to services.
The CGT-Cheminots union and others have been striking every few days since early April over President Emmanuel Macron's controversial rail reforms, causing disruption for France's 4.5 million daily train commuters.
While turn-out at the beginning was big and services were severely impacted – only one in eight TGVs were operating in the first few days of the strikes – the number of strikers has continued to decrease meaning services have been less affected as the weeks have gone by.
Their latest two-day strike, on Wednesday and Thursday, was meant to be the last but now they seem set to go on with Sud and the CGT continuing their stoppages.
However Wednesday saw the lowest number of strikers join the walk-out since the movement began on April 3rd.
Only 8.43 percent of SNCF rail workers joined the strike and ls than 32.1 percent of train drivers, with the rate having been over 50 percent for most of the period of industrial action.
On Wednesday, four out of five TGVs are scheduled to run, three out of five inter-city trains, two thirds of Transilien commuter trains around Paris, and three out of five TER regional trains. Ninety percent of international trains are expected to run.
The rail reform was a key victory in the centrist president’s push to reform wide swathes of France's economy.
Unions have been resisting plans to end life-long job security to new recruits, as well as plans to turn the SNCF into a joint-stock company, which hey saw as a first step toward privatisation despite government denials.
Macron argued that the SNCF, saddled by debts of some 47 billion euros, needs to cut costs and improve flexibility before the EU passenger rail market is opened up to competition.