Journalists at the Guardian and Observer newspapers have been asked to consider taking voluntary redundancy after they reported losses of more than £40 million in the last year.
Staff were told the two papers and their website, collectively known as Guardian News and Media (GNM), had an operating loss of £44.2m in 2011/12.
The papers, which have pioneered an open access approach to their journalism and do not charge online readers, reported a 16.3% rise in digital revenue to £45.7m in 2011/12 and saw their online audience grow 38% to 67.8m monthly unique browsers from March 2011 to March 2012.
A spokeswoman for the company said it was "on course" to save £25m by the end of a five-year programme to focus more on online publishing by 2016/17, adding: "As part of that, in editorial we aim to reduce costs by £7m to fund investment and GNM has this week re-opened the voluntary redundancy programme for editorial."
The spokeswoman said "investment in digital platforms and set-up costs for the five-year transformation programme" was partly responsible for the operating loss.
Editor-in-Chief Alan Rusbridger said: "Having the foresight to start exploring digital platforms as early as 1999 has given us a great foundation on which to build a secure future for the Guardian. This has been an extraordinary year for our journalism, all the more so for having the largest ever audience for our work."