Those cuts and other measures, which will be implemented in the coming months, are expected to save the company about $45 million a year.
"This restructuring is regrettable but warranted by changes in our industry which force us to align our cost structure with the new reality," said a statement from Pierre Karl Péladeau, president and CEO of Sun Media.
CBC News has learned some newspaper publishers and editors-in-chief have lost their jobs. Editorial staff including some reporters, editors and layout staff at some newspapers will also lose their jobs.
All union positions that have been cut will be given eight weeks of working notice, which is part of the collective bargaining agreement.
'Terrible day for quality journalism': union
The union representing more than 600 people at 13 Sun Media newspapers in Ontario criticized the decision.
"This is a terrible day for quality journalism and good paying media jobs in Canada,” said Paul Morse, president of CEP Local 87-M of the Southern Ontario News Media Guild.
"Once you kill what makes a newspaper valuable to its community by getting rid of too many of the people who help produce the quality product, you lose your audience, possibly forever."
Sun Media is the biggest newpaper publisher in Canada, with 36 paid-circulation daily newspapers and six free commuter dailies across Canada. It is a subsidiary of Quebecor Media.
The chain has multiple newspapers in eastern Ontario, including the Kingston Whig-Standard, the Ottawa Sun and various community newspapers.