Rail unions announced the possible move at the start of another two-day rolling strike which began on Monday.
"We are looking at the calendar," a union representative told the French press. "We want to warn the French as soon as possible so that they can organize their holidays."
The CGT, Unsa, Sud Rail and CFDT unions, which are due to meet mid-week, say that the possibility of prolonging the action into July and August is becoming increasingly likely.
"This government does not want to negotiate, it is them pushing us to extend [the strikes] into July and August," a union boss told the French press on Sunday.
In a interview on French television on Sunday, head of the hardline CGT trade union Philippe Martinez did not rule out prolonging the strikes but he said that it is up to "the railway workers to decide whether or not they continue their movement", which they started in early April.
At the moment the strikes are set to continue until June 28th.
Head of France's national rail company SNCF Guillaume Pepy has tried to reassure users, saying he does not believe there will be a summer strike.
He said the company will ensure trains for people taking exams before the summer break and said the strike would not continue during the summer.
"There will be no strike this summer because rail workers are responsible people," said Pepy.
Monday sees the start of another two days of strikes by rail workers over the shake-up which has been causing havoc for French commuters two days out of every five since the start of April.
Rail unions object to plans to strip new SNCF recruits of jobs-for-life and early retirement, part of Macron's bid to reduce the SNCF's nearly €50 billion of debt.
The unions are gambling on public opinion turning in their favour but polls suggest an opposite trend, with just 43 percent backing the strike in an Ifop poll released Sunday.
The scale of the disruption has also eased over the course of the month as fewer workers continue with the strike.
On Monday, 35 percent of high-speed trains are set to operate — up from just an eighth at the beginning of the month.
The strikes have caused major travel headaches for the 4.5 million daily rail users in France although they are causing less disruption than when they first started on April 3rd when only one in eight TGV services was running.