The man who launched a legal challenge to Quebec's law on unilaterally declaring independence is calling on NDP Leader Tom Mulcair to clarify his position on the province鈥檚 secession.

Keith Henderson, chair of the Special Committee for Canadian Unity, told CTV鈥檚 Power Play on Tuesday that Mulcair has a lot of explaining to do when it comes to his position Quebec鈥檚 secession. More specifically, he wants to know if the NDP would support his court challenge to Bill 99, a provincial law that claims 鈥渢he Quebec nation has the right to democratically decide its own future.鈥

鈥淒oes Tom Mulcair accept that Quebec is divisible? Would he divide Quebec territorially to take into account loyal Canadians like me who don鈥檛 want to go to a new country and aboriginals who voted 20 years ago that they won鈥檛 go into a new country?鈥

What鈥檚 his number?

At the centre of Henderson鈥檚 concerns is the NDP鈥檚 unity bill, proposed in 2013 to replace the existing Clarity Act, which sets out the conditions under which the federal government would agree to negotiate Quebec鈥檚 separation from Canada.

The NDP鈥檚 unity bill reiterates a central detail of Bill 99, which requires a bare majority -- 50 per cent plus one -- as the threshold for a successful referendum on separation. That number is concerning for Henderson.

鈥淢y number is anything that represents a clear majority that the federal government decides is adequate. It could be two thirds, it could be sixty per cent, it could be seventy-five per cent. All of those numbers are what is required for certain constitutional amendments in other countries.鈥

Henderson鈥檚 committee held a news conference Tuesday pushing Mulcair to clarify the NDP鈥檚 position on secession, two days ahead of the French televised leaders鈥 debate. He is hoping the issue comes up, as it did in the first English leaders鈥 debate on Aug. 6.

During that debate, Liberal Leader Justin Trudeau and Mulcair got into a squabble over the number of votes Trudeau would want from the Supreme Court before allowing Quebec to separate from Canada. Trudeau鈥檚 decisive answer became a highlight of the evening.

鈥淵ou want a number, Mr. Mulcair?鈥 Trudeau answered. 鈥淚鈥檒l give you a number. My number is nine (Supreme Court justices).鈥

Heading into Thursday鈥檚 debate, Henderson says the subject matter has to be approached through a wider lens to ensure that the leaders don鈥檛 get bogged down in another 鈥渨hat鈥檚 his number鈥 dispute.

鈥淭he number isn鈥檛 as important as some of the other things -- the debt, the borders, the constitutional amendment, where every Canadian has a say. That鈥檚 just as important.鈥

With files from the Canadian Press