Unions hope they can still force Macron to back down as parliament debates the draft law, with the National Assembly and the Senate moving towards a final vote as early as this month.
"This is the final stretch," said Marylise Leon, deputy leader of the CFDT union. "The endgame is now," she told the franceinfo broadcaster Saturday.
This week, Macron twice turned down urgent calls by unions to meet with him in a last-ditch attempt to get him to change his mind.
The snub made unions "very angry", said Philippe Martinez, boss of the hard-left CGT union.
"When there are millions of people in the streets, when there are strikes and all we get from the other side is silence, people wonder: What more do we need to do to be heard?", he said, calling for a referendum on the pensions reform.
"Since the president is so sure of himself, he might want to consult the people. We'll see what the response will be," he said.
"This country's leaders need to stop being in denial of this social movement," said CFDT head Laurent Berger.
Police said they expect between 800,000 and one million people at 230 planned demonstrations across France, of which up to 100,000 were likely to march in Paris where the main demonstration set off at two pm (1300 GMT).
It was the second protest day called on a weekend, with unions hoping demonstrators would show up in greater numbers if they did not have to take a day off work.
But counts around midday suggestedthe turnout could fall short of the 963,000 that protested, according to police, on Saturday, February 11.
- 'Future of children' -
"I'm here to fight for my colleagues and for our young people," said Claude Jeanvoine, 63, a retired train driver demonstrating in Strasbourg, eastern France.
"People shouldn't let the government get away with this, this is about the future of their children and grandchildren," he told AFP.
Marie-Cecile Perillat, a regional leader for the FSU union demonstrating in the southwestern city of Toulouse, said: "They're beginning to feel the pressure, including in parliament. We believe we can win, and we're not going to give up."
At the last big strike and protest day on Tuesday, turnout was just under 1.3 million people, according to police, and more than three million according to unions.
Several sectors in the French economy have been targeted by union calls for indefinite strikes, including in rail and air transport, power stations, natural gas terminals and rubbish collection.
On Saturday in Paris, urban transit was little affected by stoppages, except for some suburban train lines.
But uncollected rubbish has begun to accumulate in some of the capital's neighbourhoods, and airlines cancelled around 20 percent of their flights scheduled at French airports.
The French Senate, meanwhile, early Saturday resumed debate of the reform whose headline measure is a hike in the minimum retirement age to 64 from 62.
Senators have until Sunday evening to conclude their discussions, and a commission is then to elaborate a final version of the draft law which will be submitted to both houses of parliament for a last vote.
Should Macron's government fail to assemble a majority ahead of the vote, Prime Minister Elisabeth Borne could deploy a rarely-used constitutional tool, known as article 49/3, to push the legislation through without a vote.
An opinion poll published by broadcaster BFMTV on Saturday found that 63 percent of French people approve the protests against the reform, and 54 percent were also in favour of the strikes and blockages in some sectors.
Some 78 percent, however, said they believed that Macron would end up getting the reform adopted.