(AFP) - The French parliament was on Monday to start debating a contested pension reform championed by President Emmanuel Macron a day ahead of new strikes and mass demonstrations against the plan.

The reform is the flagship domestic policy of Macron's second and final term in office, with the president determined to implement it in the face of fierce opposition from the political left and unions, but also the wider public.

He faces a dual challenge from the street and in parliament, where his ruling party lost its overall majority in elections last year even though it remains the largest faction.

His government under Prime Minister Elisabeth Borne wants to pass the legislation with the help of the right, and without recourse to the 49.3 article of the constitution.

This article allows the adoption of a text without a vote, unless a vote of confidence is called, in a move that would risk stoking more protests.

Left-wing opponents of the administration have already filed thousands of amendments ahead of the parliamentary debate beginning on Monday afternoon.

- 'Huge mobilisation' -

Walkouts and marches are planned for both Tuesday and Saturday, although unions for rail operator SNCF said they would not call for a strike at the weekend, a holiday getaway date in some regions, and just protests.

Trains and the Paris metro are again expected to see "severe disruptions" Tuesday according to operators, and around one in five flights at Orly airport south of the capital are expected to be cancelled.

Last week's demonstrations brought out 1.3 million people nationwide, according to a police count, while unions claimed more than 2.5 million attendees. Either way, it marked the largest protest in France since 2010.

"It's out in the country that this will be settled, either by a revolt or by enduring disgust" with the government, said Francois Ruffin, an MP for hard-left France Unbowed.

"The government is no longer trying to convince people, but just to win, win by resignation and exhaustion" among opponents, he added.

With pressure growing, Borne on Sunday offered a key concession to win support from the conservative Republicans party in parliament.

While the reform will set a new legal minimum retirement age of 64 for most workers -- up from 62 -- Borne said people who started work aged between 20 and 21 will be covered by an exemption allowing them to leave earlier, at 63.

Calling the offer a "band aid", the head of the CFDT union Laurent Berger said that the move "isn't the response to the huge, geographically and professionally diverse mobilisation" that has swept France.

But Republicans chief Eric Ciotti told the Parisien newspaper that he would back the reform, potentially securing a majority for the government.

- Keep seniors working -

After an attempted 2019 pensions reform that was stymied by the coronavirus crisis, the changes mark another step by reformist Macron in aligning France with its EU neighbours -- most of which already have higher retirement ages than the proposed 64 years.

He and his ministers aim to get the pensions system out of deficit by 2030 by finding around 18 billion euros ($19.5 billion) of annual savings -- mostly from getting people to work for longer and abolishing some special retirement schemes.

But while Borne and others have insisted theirs is a fair reform, critics say that women will on average have to wait still longer for retirement than men, as many have interruptions in their careers from childbearing and care responsibilities.

Opponents also say the reform fails to adequately account for people in physically strenuous jobs like builders and doesn't deal with companies' reluctance to hire and retain older workers.

Borne said the government would pile pressure on companies to end the practice of letting go of older employees, which leaves many struggling to find work in their final years before pension age.

"Too often, companies stop training and recruiting older people," Borne told the JDD weekly on Sunday.

"It's shocking for the employees and it's a loss to deprive ourselves of their skills."

© Agence France-Presse