Socialist opposition leader Lionel Jospin urged conservative Prime Minister Alain Juppe to drop the bill, which he said was "despicable" in spirit and "useless" in practice.
"Rather than further toughening laws that turn out never to be effective, we propose concentrating on [attacking] the organization of illegal labor, which would dry up an important source [of illegal immigration]," Jospin said.
As a politician, he could not advocate civil disobedience, Jospin said, but as a "private citizen" he could not imagine reporting to the police if a foreign friend left his home.
The influential, conservative-dominated French Mayors Association said the proposed measure would be ineffective. The association called for an amendment leaving it solely to the state to check whether foreigners respected the terms of their visas.
The left-wing daily Liberation, which called Monday for a million protest signatures before the National Assembly gives the bill a second reading next Tuesday, published four pages of names of intellectuals, elected officials and professionals who opposed the legislation or called for civil disobedience.
New petitions sprouted like mushrooms with magistrates and psychologists joining the ranks of protesters.
The 59 film makers who signed the original appeal last week against Interior Minister Jean-Louis Debre's bill included several supporters of the center-right government.
Juppe stood by the bill in a radio interview Monday, calling it "balanced" and accusing critics of playing into the hands of the extreme-right National Front.
But he left himself an emergency exit, saying it was up to parliament in its wisdom, subject to approval by the Constitutional Council, to make the law.
A senior parliamentarian in Juppe's Gaullist party, Pierre Mazeaud, called a news conference for Wednesday to offer a "solution" to the dispute.
An amendment by Mazeaud, chairman of the parliamentary legislation committee, could get the government off the hook.
Civil rights and anti-racist groups, backed by the left-wing opposition, have called demonstrations for Saturday and next Tuesday, when the bill returns to the National Assembly.
The National Front, which advocates expelling three million immigrants, derided the bill as a "half-measure."
The Front's No. 2, Bruno Megret, said in a radio interview: "The intellectuals are totally cut off from the people. They all agree with each other in the near-totalitarian conformism that reigns in the French intellectual classes."
Megret called the bill "a little half-measure which everyone knows will change nothing and shows the government is pursuing a botched policy of half-measures that provoke major opposition. ... This is a severe sign of degeneration."
He said the government should tighten controls on France's borders instead of counting on citizens to do its job.
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