Anna Andersson vice chairperson of the nursing union Vårförbundet said exhausted nurses can put patients' lives at risk:
"Many are working very long shifts and if you've had too many overtime shifts without a rest there's a bigger chance of making a mistake," she told SVT news.
Stockholm County Council, which runs the region's hospitals, has struggled to get staff to cover summer vacations and see summer as the main problem period for overtime.
But the county's personnel manager, Maria Englund, does not share the nursing union's fears that overworked nurses are a growing safety risk.
"I'm sure that the right measures are being taken out on the wards to avoid landing in a situation where staff are overworked and feel that they cannot go on anymore," she said.
But according to one nurse who spoke to SVT, that point has long passed. Gabriella Eklund at Karolinska Hospital said the management at the county level were not taking patient safety seriously and that hospital were being kept going by staff loyalty.
That is a view echoed by the national nursing union.
"We're used to doing everything we can to put the patients first and providing safe care," said Anna Andersson.
"But now things have gone so far and we're so overworked and exhausted that our members have started to say that this can't go on any more."