Mainstream right MP Eric Ciotti accused Macron of repeating the offences of the last governlent's justice minister, Christiane Taubira, whose efforts at criminal justice reform were bitterly resisted by the right.
The president should be building more prisons, so that sentences can be served, rather than reducing the number of prison sentences, Ciotti said on Wednesday.
The far-right National Front also invoked the spectre of the former justice minister, calling Macron's plan "Taubira, only worse".
"With Macron it is not criminals who are convicted but honest folk," a party statement said.
On the left, the Communist Party claimed the president's proposals were just window-dressing.
"The question of a penal system that is centred on prevention and the return to society of people who have one day been convicted remains unanswered," it said in a statement.
While visiting a prison officers' training school on Tuesday, Macron unveiled the first proposals in what he promises will be a major overhaul of the criminal justice system.
The proposals that have outraged the right are that sentences of less than a month be abolished and that sentences of less than six months could be served outside prison, for example through electronic tagging.
But Macron also called for an end to the current practice that means offenders sentenced to less than a year do not go to prison.
And he said that all offenders sentenced to over a year should be placed behind bars.
France has been repeatedly criticised by the European Court of Human Rights for overcrowding in its prisons, which is 120 percent on average and as high as 200 percent in the Paris region.
A report commissioned by the previous, Socialist government dubbed conditions inside "inhuman and degrading".
But attempts to increase non-custodial sentences have so far failed to resolve the crisis.
Macron's proposals are based on the principle that overcrowding is concentrated in prisons where short sentences are being served.
"In January 2001 there were almost 48,000 prisoners in France, that is an incarceration rate of 75.6 inmates per 100,000 inhabitants," he said on Tuesday. "Today we have nearly 70,000 prisoners in our country, that is a rate that nearly reaches 100 inmates per 100,000 inhabitants."
Prisons are now "schools for crime" where "violence grows", Macron said, claiming that his proposals are a third way between laxism and repression.
The chair of the parliamentary committee preparing the reform, Yaël Braun-Pivet, defended the plan on Wednesday, saying it was "anything but soft on crime".
Braun-Pivet, an MP for Macron's Republic on the Move party, pointed out that 40 percent of former prisoners return to crime and said that the prison system responsible for that figure is "clearly not the ideal solution".
The committee's report will be published on 21 March.
Prison officers' protests
Macron has declared his support for the previous government's plan to create 15,000 extra prison places but has been forced to accept that only 7,000 will be created during the course of his five-year term.
Protests by prison officers last month led the government to promise better pay for a service that currently has 2,500 vacancies and special unit for "radicalised" inmates.
The government also hopes to expand the probation service and give prisoners the right to vote.
France's penal policy in figures:
- France is one of the few west European countries whose prison population continues to rise, although its jails are less overcrowded than those of Belgium, which rents spare places off the Netherlands;
- At one prison officer for every 2.5 inmates, France has one of the lowest proportional staffing rates;
- It has 88 prison places per 100,000 head of population, compared to a European average of 130;
- Some 97 percent of prisoners are men, only 2,500 women are behind bars;
- Of the 550,000 people found guilty by courts in 2016, 52 percent were given prison sentences;
- Only 11,000 convicted offenders serve their terms outside prison, usually by wearing electronic tags, while only three percent of those convicted were sentenced to community service.