The Employment Law Advisory Services said the first Monday in February, labeled "National Sickie Day," has historically found businesses short staffed as employees tell their bosses they are too sick to come in, Sky News reported.
"Poor weather, long dark nights and a general dissatisfaction with official holidays all mean that early February is a very popular time for workers to give themselves an extra 'duvet day'," said Peter Moone, spokesman for the Employment Law Advisory Services.
"Add that to the fact that almost three quarters of the country's skivers prefer to fake illness on a Monday, and that makes today the worst day of the year for employers."
However, union officials say claims that employees are faking sick are "insulting."
"February is slap bang in the middle of the cold and flu season and to suggest that the thousands of employees who are genuinely off ill today are throwing a 'sickie' is hugely insulting," said Brendan Barber, general secretary of the Trades Union Congress.