Employers will have to change the way they treat overweight staff following a European Union court ruling that obesity can, in severe cases, constitute a disability.

The landmark decision by the European Court of Justice – in the case of a Danish childminder who lost his job – establishes a precedent that could affect employment rights across the continent. It stops short, however, of declaring obesity to be a protected characteristic against which all discrimination is prohibited.

The complex reasoning did not resolve the case in dispute: the claim by Karsten Kaltoft, who was dismissed by his local city council in 2010. The Luxembourg court referred the claim for compensation back to a Danish court to determine whether Kaltoft’s obesity falls within the definition of disability.

The court heard that Kaltoft weighed over 160kg (25st). His lawyers argued that his weight was one of the reasons he lost his job and that it amounted to unfair discrimination. His employer, Billund city council, has denied that obesity was among the reasons for Kaltoft’s dismissal.

Kaltoft, 50, who is married with two children, told the Guardian: “It’s a victory. It’s taken a long time to get here and I will still have to go through the local court. I was fired because [the council said] I was too fat. I hope the Danish court will eventually rule that that is not OK.

“I had been a childminder for 15 years. Everyone told me I did a good job. I don’t think it was fair [to sack me]. I was already overweight when I got the job. I’m fat. It’s not a lifestyle choice; it’s just the way I am. Most overweight people want to be thinner.” Kaltoft is now working as a lorry driver.

His lawyer dismissed stories that Kaltoft was so large he could not bend down to tie his shoelaces as smear tactics. Kaltoft had, however, repeatedly been asked by the council to lose weight.

His lawyer, Jacob Sand, pointed out that the judgment did not distinguish as to how anyone had become obese. “This ruling clearly establishes that the notion of disability is to be construed to the effect that clinical obesity also may qualify as an impairment enjoying protection under the relevant rule,” he said. “It is the first time ever that a case has been brought at EU level regarding protection as a result of clinical obesity.

“The ruling implies that there will be a shared burden of proof in relation to the discrimination of employees suffering from clinical obesity and that employers in relation to this group of employees will be obliged to initiate appropriate measures in order to remedy any functional defects.”

The judgment is being carefully examined by employment lawyers since decisions by the ECJ are binding across the European Union. In its judgment, the court said: “While no general principle of EU law prohibits, in itself, discrimination on grounds of obesity, that condition falls within the concept of ‘disability’ where, under particular conditions, it hinders the full and effective participation of the person concerned in professional life on an equal basis with other workers …

“Such would be the case, in particular, if the obesity of the worker hindered that participation on account of reduced mobility or the onset of medical conditions preventing that person from carrying out work or causing discomfort when exercising professional activity.”

Responding to the decision, Matthew Elliott, chief executive of Business for Britain, which campaigns to change the terms of the country’s EU membership, said: “This ruling could place a huge burden on UK businesses, with employers forced to pick up the bill for the increased waistlines of their workforce.

“This is yet another example of a decision by an EU court with no thought for the consequences or impact on business and the wider economy. “

Tam Fry, spokesman for the National Obesity Forum, said: “This has opened a can of worms for all employers in this country. They will be required to make adjustments to their furniture and doors and whatever is needed for very large people. I believe it will also cause friction in the workplace between obese people and other workers.” One in four adults in the UK is obese, according to latest figures from the NHS.

Omer Simjee, Employment partner at Irwin Mitchell said: “This is a significant ruling and although being ‘fat’ is not enough in itself to be considered disabled, it could if it restricts an individual’s ability to actively and fully engage in their work. That said, it would appear as though there does not need [to be] an underlying medical condition. This is new and will in appropriate cases mean that obesity in its own right can be deemed to be a disability. With one in four adults in the UK being classed as obese, this represents a major headache for UK businesses.”

Naeema Choudry, partner at law firm Eversheds, said: “[This] decision clarifies that, under the European Equal Treatment Framework Directive, obesity is not always a disability per se, but it is a condition which can give rise to discrimination protection.

“Each case must be looked at on its own merits to determine the presence of long-term mental or physical impairments. While obesity is likely to increase exposure to such impediments, therefore, the effect of individual obesity is the critical question, not the degree of obesity.”

Vanessa Di Cuffa, employment law partner at Shakespeares, said: “This is the right decision. Although previous legislation allowed for employees to be protected against other forms of discrimination, it is positive that obesity is now being seriously recognised. Previously, severely obese staff could only seek for suitable workplace provisions to be made under associated conditions such as diabetes, respiratory problems or mobility impairment.

“Employers should continue to promote healthy lifestyles and extend support to workers who are actively trying to reduce their weight. It is right that the EU has moved forward with enshrining this into law. However, employers must continue to, or start, providing appropriate support to staff with obesity issues at any level.”

Julian Hemming, employment partner at the law firm Osborne Clarke, said: “This ruling is a real problem for employers – it’s still not clear enough for them to be sure that they’re going to be on the right side of the law. While the ECJ does not consider obesity a disability in itself, businesses could still face discrimination claims from obese staff if their weight problem is of such a degree that they fall within the definition of having a ‘disability’ in the legislation.”