Long-term sickness absence has increased in one third of organisations, according to latest research.
The 2009 Sickness Absence survey by manufacturer's organisation EEF and insurance provider Unum found 36% of the 697 organisations surveyed reported a rise in the number of employees being off for more than one month between 2007-8.
About a third of long-term absences were caused by waiting for "surgery, medical investigation or tests", after being diagnosed with back problems (34%), cancer (26%) and stress (25%).
Sayeed Khan, chief medical adviser at the EEF, said: "Employers can do a lot to address this through better management, but employers would benefit from faster access to NHS treatments and secondary care in order to have a chance of significantly improving absence levels."
Sickness absence had improved in the manufacturing sector, with three million fewer days lost in 2008 compared to 2005. But Khan said the improvement in the number of sick days should not be overstated.
"The overall fall in sickness absence figures conceals a worrying trend - an ongoing issue with long-term absence," he said.
Of those employers who saw an increase in long-term sickness absence, more than a quarter (28%) reported that "waiting for appointment or diagnosis of illness" was a barrier on the pathway to return to work.
Professor Michael O'Donnell, chief medical officer at Unum, said the 'fit note', expected to be introduced later this year to replace the sick note, would help to improve absence rates as it would list what employees could do at work while they were awaiting treatment.
"The sooner we can introduce the fit note, the better," O'Donnell said. "Changing the mindset and therefore attitudes [of employees and employers] is the critical first step in bringing about a real and effective change in approach by all parties. There is still a need for early intervention in the working population to prevent job loss and long-term absence from work."
Nearly half of all companies polled said they were dissatisfied with the current sick note system.