Stéphane Bédard pointed to the four years Couillard spent in Saudi Arabia the 1990s working as a doctor. The country is governed by Shariah law.
"We're asking him not to import that reality here," he said.
Bédard suggested Couillard's experience had sensitized him to Saudi values and that is why he won't address the secular issue right now.
The premier, who is currently in Davos, Switzerland attending the World Economic Forum, said Bédard's comments went too far and "border on defamation."
Couillard said the PQ is resorting to throwing mud.
Visibly irritated, he said he could take Bédard to court, but doesn't want to "lose time" with "such a person."
Couillard says he believes the accusations are a way for the PQ to distract people from the leadership race and the sovereignty question.
No confirmation on when bill will be tabled
There has been a lot of back and forth within the government recently over when it will table religious neutrality legislation.
On election night in April, Couillard said he would deal with the secular issue as soon as possible.
Last week, the justice minister said she would table a bill between now and the end of the session in June.
Then, while abroad, the premier backed away from that deadline, saying a bill would be tabled before the end of the Liberals' mandate in 2018.
Yesterday, Couillard said that legislation could be tabled before the end of this session.
The PQ is trying to put pressure on the Liberals to address the secular values question as soon as possible.
During their caucus meeting, PQ MNAs said they would make it a major focus when the National Assembly reconvenes in February.