Fake fit notes which claim to be "authentic looking replicas" of the genuine forms are being circulated for as little as £10.
The website Doctorsnotestore.com is openly selling fake versions of the new fit notes - introduced in April - which are described as "authentic looking replica doctors sick note or medical certificates. Written on official doctors' notepaper, with real stamp."
The fake fit notes come with a guaranteed 48-hour delivery, and employees can choose to have their notes stamped by doctors from medical centres in any UK city.
While the website claims the documents are "for novelty use only", an employee could try to use one to claim sick pay.
Employment experts have warned HR could be scammed by the fakes as they are still getting used to the new fit-note system.
Katherine Ashby, a researcher in the health and wellbeing team at The Work Foundation, told Personnel Today: "It's a risk that employers could be fooled by them because the fit note is a new concept."
Ben Willmott, employee relations adviser at the Chartered Institute of Personnel and Development, agreed it could be "very difficult for employers to spot them", but said if HR were suspicious, they should refer the worker to an independent occupational health adviser or doctor, or alternatively call the surgery which issued the note to check its legitimacy and that it was signed by the doctor named. He added employers could also warn their staff that anyone found using the fakes would face disciplinary action.
Willmott added concerns about job security meant most employees were conscious about reducing their sickness absence during the recession and so would not use the fake documents, but he warned those still tempted to use them to claim sick pay that they would be committing fraud.
A CBI/Pfizer sickness absence report published today found the average number of sick days taken during 2009 had dropped to the lowest level on record.
But to entice workers, Doctorsnotestore.com is currently running a special 'buy one, get one free' offer with a blank fit note, so they will "have a spare one to fill in yourself at a later date - you never know when you'll have to explain your absence again".
To complete the note, the employee just has to supply their name and address, what they are suffering from, and the date they started to suffer the problem.
In 2008 Personnel Today reported that the Doctorsnotestores.com website was selling fake sick notes for £24.99.
The government launched the new fit note in April in a bid to help employers reduce sickness absence and help people on long-term sick leave return to work.