UK bosses suspect that one in eight of all UK workplace absences are due to staff faking illness, research by the CBI suggests.
Most absences are genuine, the TUC says
Managers told the CBI they believed many employees faked illness to take a Monday or Friday off work.
It said employers must clamp down on staff taking "sickies" which it said cost the economy about £1.6bn.
About 400 employers were surveyed. They said they believed that 12% of days off taken by workers were not genuine.
But in response, the TUC said that "unsympathetic" bosses meant many ill employees went to work.
The survey suggested there was a correlation between absences and major sporting events.
Overall workplace absence, including genuine illness, cost the economy about £13.4bn in 2006, the CBI added.
Workers took an average of seven days off sick in 2006, it said.
This was about half a day more than in the previous year and equated to the loss of 175 million working days.
Public sector workers had the highest average absence at nine days per worker.
This was 44% higher than in the private sector, despite government efforts to trim the number of days taken off sick, the CBI said.
Some workers felt they had the right to use sickies to give themselves a long weekend or a longer holiday, said the CBI's director of human resources policy, Susan Anderson.
As well as the financial burden, this put pressure on colleagues, she said.
"Everybody gets sick and employers understand that most absence is genuine," Ms Anderson said.
"It is in no-one's interest if staff come to work when they are not well," she said.
"But there is a culture of absenteeism in some workplaces that must be addressed."
The variation in absenteeism showed that some firms were managing the problem better than others, she added.
But TUC general secretary Brendan Barber said that most people who took time off sick were genuinely ill.
Staff often came into work when sick because of the "unsympathetic" attitude of bosses to people phoning in sick, he said.
"Every organisation should have a sickness absence policy that allows staff to take days off work without feeling guilty as well as dealing fairly with the tiny minority who take sickness leave that is not genuine," Mr Barber said.
Last year, the Amicus union was involved in a row with employers after it was accused of advising people how to take sickies to watch the World Cup.
On its website, the union said it was "difficult to prove someone is not really sick" and offered a line of defence to workers who are caught out.