A row over workers taking sickies during the World Cup blew up yesterday after a trade union came under attack for allegedly offering advice on how to get away with skiving.
Amicus was criticised for posting an article on its website which said it was difficult to prove that someone was not really sick if they had one day off.
Stephen Alambritis of the Federation of Small Businesses called for the union to withdraw the advice.
Employers were already taking action to be "very, very flexible" in allowing staff to structure working days around matches, he suggested.
Encouraging sickies - and suggesting it was possible to get away with it - was grossly unfair on firms and fellow workers.
"They should withdraw that bit of advice from the web," he said.
"It's grossly unfair also on staff who are not football fans when they see a union advising their other colleagues to take a sickie."
Amicus said it was not suggesting workers should take sickies, and accused business groups of "over reacting".
A spokesman said: "It is ludicrous to say we are condoning workers taking a sickie. We understand the temptation and excitement but we are actually encouraging employers and employees to work together to find the best way of allowing staff to watch games if they want to.
"We need employers to be flexible but our message to workers is that if your boss is a Scrooge don't be tempted to take time off during the World Cup."
Amicus general secretary Derek Simpson said later: "We are not encouraging staff to take a sickie, we are advising them not to, and warning them of the consequences.
"Employees who want to watch the World Cup should make the appropriate arrangements with their employer."
The advice on the union's website said: "Taking time off work without permission can lead to dismissal."