Canadian author Margaret Atwood and singer-songwriter Sarah Harmer are voicing complaints about the Conservatives' proposed anti-terrorism bill, asking Liberal MPs from their communities to vote against it.

In particular, Harmer and Atwood have got their backs up over the Liberals' pledge to support the bill, despite saying they would change it if they win power in next fall's election.

"[Prime Minister Stephen Harper] is attacking our rights & freedoms," Atwood tweeted at Toronto MP Adam Vaughan, a Liberal.

"Please do the right thing and #voteagainstC51."

Harmer retweeted Atwood's message, tagging Kingston, Ont., Liberal MP Ted Hsu.

“<a href="https://twitter.com/MargaretAtwood">@MargaretAtwood</a>: Stephen Harper is attacking our rights & freedoms. Please do the right thing and <a href="https://twitter.com/hashtag/VoteAgainstC51?src=hash">#VoteAgainstC51</a>, <a href="https://twitter.com/TOAdamVaughan">@toadamvaughan</a>" <a href="https://twitter.com/tedhsu">@tedhsu</a> —@sarah_harmer

The NDP and the Green Party oppose C-51, which has gone through the committee stage in the House of Commons and is set to return to the floor of the House next week.

The legislation is a late-bloomer in this session, having been tabled less than a year before the 2015 election.

The NDP is using procedural tactics to delay the bill and has tabled 66 deletion motions which could, depending on how the votes are grouped, slow the House agenda. The party is also asking its supporters to go directly to Liberal MPs to tell them to vote against the bill.

Sweeping powers

Opponents argue the pendulum has swung too far toward security and away from civil liberties.

Bill C-51 would grant sweeping police powers to the Canadian Security Intelligence Service (CSIS), the country's spy agency, without increasing oversight. The government says some measures would require a judge to sign off, but critics point out that only happens if a CSIS agent feels it is necessary.

The bill would lower the threshold of evidence for arrests: it would let law enforcement agencies arrest somebody if they think a terrorist act "may be carried out," instead of the current standard of "will be carried out." It would also increase the period of preventive detention from three days to seven and make it illegal to promote terrorism.

The NDP and the Liberals proposed a number of amendments at the committee stage, but the Conservatives voted them down.

After public protests and extensive criticism, the government allowed a handful of changes to the bill that:

Removed the word "lawful" from the section listing exemptions to the new counterterror measures addressing protests. Many had feared peaceful protesters engaged in civil disobedience could be caught up in the law, arguing it could just be moral disorder that leads to unlawful but peaceful protests.

Clarified that CSIS agents, while newly empowered to "disrupt" potential threats, will not be able to make arrests.

Established limits on inter-agency information sharing.

Adjusted a provision that would have given the public safety minister the power to direct airlines to do "anything" that, in his or her view, is "reasonably necessary" to prevent a terrorist act.

Other measures would allow CSIS agents to disrupt activities they believe are related to terrorism, subject only to limits such as a ban on causing bodily harm or violating a subject's sexual integrity.

'Minds are changing'

Opponents of the bill held a day of action in March that in some cities drew hundreds, and plan another day of protests this weekend.

NDP candidate Jennifer Hollett, who is nominated to run in Toronto's University-Rosedale riding next fall, said she's pleasantly surprised at how mainstream an issue C-51 has become.

"It's become a larger issue of human rights and freedoms, and a look at who we are as a country," she said.

Hollett said the NDP hopes the Liberals will change their minds and oppose C-51, adding that if the opposition could convince a handful of Conservative MPs to oppose their own government's legislation, the opponents could block the bill.

"Public opinion is shifting — we've seen that in the polls. I know that that does matter to Prime Minister Stephen Harper as well as [Liberal Leader] Justin Trudeau. Minds are changing."

Hsu, Vaughan and the Liberal Party declined to comment.