But getting the government to double the number of planned hearings on the bill and bolster the witness list didn't prevent the New Democrats from bogging down committee efforts to establish the scope of the study.
Bill C-51, introduced in January, seeks to increase the powers of police and spy agencies in the name of fighting terrorism.
It's a marquee piece of legislation for the Conservatives, part of the party's broader tough-on-crime agenda in an election year, and they say it provides crucial tools to crack down on would-be terrorists.
"Now is not the time for the NDP agenda of attacking the police and the security agencies," Harper said during question period.
"We have serious problems in this country. Now is the time to take on the terrorists and that is what we're doing."
The Tories called it a charade that the NDP was demanding 25 hearings on the bill and nearly 100 witnesses, considering the party has already made it clear it won't support the legislation.
The New Democrats say the bill is too broad and vague and its provisions wouldn't have prevented the October attacks in Ottawa or Quebec, nor deal with the growing problem of Canadians leaving the country to join extremist groups.
"The Conservatives are more interested in scoring political points than in preventing radicalization," said New Democrat MP Rosane Dore Lefebvre.
Initially the Conservatives had sought to hold just four meetings on the bill — one with the federal ministers for justice and public safety, along with their bureaucrats, and three others with so-called expert witnesses.
Thursday's negotiations saw them agree to nine meetings altogether, with 50 witnesses in total.
But the New Democrats kept debate on the proposed hearings going for hours longer than scheduled by exploiting the lack of a time limit on certain elements of committee debate in their bid to get more witnesses and meetings.
Among others, the NDP wants to hear from the RCMP, CSIS and regular Canadians whose lives are affected by the issue, while respecting the Conservatives' goal to get the bill out of committee by the end of March.
"We'll sit nights. We'll sit weekends. We'll sit during the constituency weeks if we have to," said NDP public safety critic Randall Garrison.
"The government says this timetable is necessary. We've agreed."
The NDP's filibuster tactics are little more than shallow political gamesmanship, Tory MP Rick Norlock said as he pleaded for an end to the day.
"This is getting ridiculous," he said. "Anybody who has followed it so far can see through all the horsepucky that is coming out."
The Liberals were backing New Democrat demands, saying in the wake of the 2001 terrorist attacks, their government passed sweeping new measures after 19 full days of committee study.
"(This) is no less serious," Liberal MP Bill Casey said of the latest bill. "It is no less worthy of our time and effort."
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