Staff at the two local newspapers have been without a contract for 34 months.
Postmedia said in a letter that it will consider permanent job cuts if a labour disruption happens
Executive chairman Paul Godfrey said that the revenue declines from its legacy business had slowed and the company "is making some progress" from its digital advertising initiatives.
November deal led to the closure of nine Ottawa newspapers and dozens more across Ontario.
Canada's largest newspaper chain, which publishes the Ottawa Citizen and Ottawa Sun says revenues fell 10.3 per cent to $189M.
Meanwhile, union and opposition party leaders are urging the federal government to step in to aid the struggling print industry.
Metro Ottawa, Kanata Kourier-Standard, Nepean/Barrhaven News, Stittsville News, Orleans News, and Ottawa East, West and South News all set to close by mid-January
Unionization drive follows a controversy over bonuses paid to several top Postmedia executives while the company cut staff.
Postmedia Network Canada Corp. is reporting a $13-million net profit in its fiscal third quarter, as cost savings more than offset an 11.1 per cent decline in overall revenue.
Staff at Ottawa’s two major daily newspapers have voted 91.3 per cent in favour of giving their union a mandate to strike against employer Postmedia, according to a union representative.