Unison says two-thirds of employers have recently introduced measures to tackle absenteeism, including spot checks on staff who say they're too ill to go to work, and interviews when they return.

Research commissioned by the union showed some staff in the health service, local authorities and in public utilities were being contacted at home by their managers to check up on their illness.

The "punitive" policies being introduced by managers have backfired, the union says, because it is fostering stress and even more sickness absence.

Head of Health and Safety, Sarah Copsey, said persistent misuse of sick leave should be dealt with because it added to pressures on other staff.

Unfair to genuine cases

But she said: "We are concerned at a growing trend that all staff sickness absence is being treated as malingering and that the procedures are unfair to staff who are off with genuine sickness.

"Policies which can appear fair on paper are often harsh, arbitrary and inconsistent in practice. We have examples of staff falling foul of procedures following time off with post-natal depression or heart attacks."

Unison is producing guidelines

Ms Copsey said in one case a car park attendant in London who was off sick after a car ran over his foot returned to face a discipline charge over his absence.

The union also warned that some staff were being forced to stay at work even when they were ill, increasing the threat of infections being passed on to colleagues.