The confrontation is over a government bill intended to bring French protection of copyright of digital content into line with a 2001
European Union directive.
The debate could conceivably result in a seachange in the way countries in Europe attack the problem of the online "theft" of commercial works.
MPs who debated an earlier version of the bill in December have already voted for amendments that would make downloading legal if Internet users paid a small monthly fee. The fee would pay for artists' royalties.
But Prime Minister Dominique de Villepin's centre-right administration is doing everything to quash that initiative.
The parliamentary leader of the opposition Socialists, Jean-Marc Ayrault, said the government's strong-arm tactics reeked of "panic".
On his side are several members of the majority ruling UMP party who still appear to back legalised downloads.
Several days of sharp debate are expected before a vote due on March 15, one day later than previously announced.
If MPs succeed France would join a small number of Western countries, including Canada and the Netherlands, which allow consumers to legally make copies of copyrighted digital files for private use.
That would pit them against many other countries, most notably the United States, which have passed legislation expressly outlawing the practice.