Couillard challenged all of Quebec's political leaders to open up their books to the public on Tuesday at a news conference in Trois-Rivières.
"I will divulge not only my 2012 tax return from when I was in the private sector, but also the financial record of my assets and my spouse's. This information will be available on the Liberal website before Thursday morning," Couillard said.
Couillard said he wanted to demonstrate his transparency and integrity.
Marois quickly confirmed she wouldn't be releasing those documents publicly and criticized Couillard for trying to distract voters.
"Mr. Couillard is trying to create a diversion, because he has nothing else to offer in terms of integrity," Marois said to journalists in Blainville, Que.
"The answer is no ... The ethics commission has received all the documents that I and my spouse needed to provide and it was very satisfied. Besides that, the salary of the premier is already public," she said.
The premier of Quebec receives an annual remuneration of $184,398, according to the website of the national assembly.
Coalition Avenir Québec Leader François Legault and Québec Solidaire Leader Françoise David both said they would be willing to make their financial records public if all the other leaders agreed to do the same.