Workers suffering from ill-health could be forced back too soon if the Government accepts recommendations aimed at tackling long-term sickness absence, union leaders have warned.
An independent review said that under the current system, people were often "pushed away" from work, with little support for returning to their job quickly.
The review recommended a new Independent Assessment Service that employers and GPs can refer long-term sickness absence cases to for advice, claiming that employers could save around £100 million a year from reductions to sick pay bills.
TUC General Secretary Brendan Barber said the current method of sickness absence certification and pay was not in need of a major overhaul.
"Unions are concerned that however well-intended this report, there is a danger it will be seized upon by some rogue employers as an excuse to force people back to work before they are good and ready.
"The report also fails to address the huge issue of "presenteeism" where workers come in to work when they should be off sick, despite evidence that this is a major and growing problem in the workplace."
Business leaders welcomed the recommendations, saying that 70% of firms believed that the rules on how to handle sickness absence were burdensome.
John Longworth, Director General of the British Chambers of Commerce, said: "The existing 'fit note' system does not work for business. Since employers want individuals back in the workplace as soon as they are able, the proposal for a thorough assessment at four weeks will boost employer confidence.
"Most people who are off sick could undertake some duties, so the new system will get them back into work sooner, benefiting individuals, businesses and the economy as a whole. Ministers must focus on implementing the new assessment and the other measures recommended by this review quickly, to make sure everyone who can work, does work."
Professor Sayeed Khan, Chief Medical Adviser at Engineering Employers Federation, said: "This is a welcome step forward for both employers and employees which should make a marked difference to waiting times for assessments and, help make further inroads into reducing sickness absence."