Today’s results showed the regional publisher shed 609 jobs during 2013 and has now lost 1,600 over the past two years.
Bosses have hailed the results, which also showed underlying operating profit increasing for the first time in seven years, as a sign that the company has turned the corner.
But the NUJ said the staff that remain are now struggling with an “unacceptable” workload which was making it harder to maintain quality journalism.
Hundreds more staff are expected to leave JP this year as a result of the company’s enhanced voluntary redundancy package introduced last autumn.
The scheme has helped JP reduce its net debt from £320m to £302m at the end of 2013.
The NUJ’s national organiser Laura Davison said: “While the union welcomes Johnston Press’s first profit increase in seven years, we do not welcome the fact that it has been made as a result of a huge cull of journalists’ jobs.
“Local newspapers need quality journalism and quality journalists and this is made difficult when experienced staff go and those who remain struggle with an unacceptable workload. The signs are that hundreds more jobs could go this year.
The JP group chapel said in a statement: “The continuing strangulation of the company through debt and interest charges is coming at a high cost for Johnston Press staff. We now know the sheer scale of the numbers who have left the company.
“Journalists have seen colleagues leaving in droves and are facing increased workloads alongside cuts to terms and conditions. That is not a sustainable situation.”