French Interior Minister Bernard Cazeneuve refused to be intimidated by comments made on Sunday by Italian authorities, including Prime Minister Matteo Renzi.
"If Europe chooses solidarity, good. If it doesn't, we have Plan B ready. But it would first and foremost hurt Europe," he added, without providing details.
In response, Cazeneuve told French channel BFMTV that Italy had no choice but to follow the rules.
"The Dublin rules must be respected. When migrants arrive in France that have been through Italy and registered there, the European law applies and that means they must be returned to Italy," he said.
"They do not have the right to pass and must be handled by Italy."
Under the Dublin convention, refugees must apply for asylum in the first country of entry to Europe -- a rule which Italy says is unfair as it leaves Rome to deal with the thousands of migrants washing up on its shores. Greece has also long complained of being left with the same problem.
Cazeneuve noted that around 15,000 migrants were sent back to Italy last year, but that the figure had shot up this year after he ensured economic migrants were turned back to the country in which they had arrived.
"This needs to be done to ensure the welcome of those who are refugees. There needs to be a firm policy," he told the channel.
Italy has been struggling with an increase in the number of migrants arriving on the shores from across the Mediterranean Sea. Over 57,000 migrants and asylum seekers have been rescued at sea and brought to Italy so far this year, thousands more than at the same time in 2014.
Renzi has said he will raise the matter with his British and French counterparts when they travel to Milan this week, as well as speaking to European Commission head Jean-Claude Juncker and German Chancellor Angela Merkel.