Even though Mr Macron was re-elected last year on a platform of retirement reforms, his ruling coalition has no majority in the Assembly and would have needed support from the Republicans party to pass the pension changes.
Officials from Mr Macron's Renaissance party spent the morning desperately whipping members into line in a bid to pass their bill.
They knew some of their MPs could vote against or abstain, faced with the evident unpopularity of the bill, so they resorted to special constitutional powers.
But whenever a government invokes the 49:3, it can be sure it will be accused straight away of riding roughshod over the will of the people.
In fact, it has been used precisely 100 times in the more than 60 years of the Fifth Republic, and by governments of all shades.