Working while on sick leave, even when compatible with the condition: the second route to lawful dismissal
When we explained how a worker on sick leave is investigated, we set out one essential rule: it isn't enough to photograph someone "doing things."
Someone on sick leave can walk, drive, go out for lunch, travel, or carry out activities compatible with their recovery.
But there is another, especially important scenario: the employee who, while on sick leave, doesn't limit themselves to everyday activities, but actually works.
There, the analysis can change completely.
A recent ruling by the TSJ (High Court) of Catalonia, handed down in late 2025, once again put the spotlight on a doctrine our case law has upheld for decades: genuine work activity, whether self-employed or for a third party, carried out during a period of temporary incapacity can amount to a serious breach of contractual good faith even if that activity doesn't medically harm recovery.
The case
An employee was on temporary incapacity leave, and there had been an earlier labour dispute.
The company commissioned a private investigation to find out what activities she was carrying out while on leave.
The report documented domestic cleaning work performed for third parties.
The company proceeded with a disciplinary dismissal.
The employment tribunal (Juzgado de lo Social) focused its analysis on whether the activity harmed her recovery, and ruled the dismissal unfair.
The TSJ corrected that approach: the question wasn't only whether cleaning medically harmed her condition, but whether the employee was carrying out genuine work activity while her contract remained suspended due to incapacity.
Two main pathways
First: conduct harmful to recovery
This is the classic scenario.
The employee engages in conduct that may delay healing, aggravate the injury, contradict medical treatment, or endanger recovery.
Here, the relationship between the condition and the activity is essential.
The investigator documents the type of movement, loads, repetition, duration, intensity, and continuity. It will then be for the medical professional and the court to determine the clinical relevance.
Second: conduct that reveals working capacity or amounts to genuine work
The activity may not be harmful to recovery and yet reveal a working capacity that is difficult to reconcile with a state of incapacity.
And the analysis becomes even more intense when what is proven isn't a personal activity, but genuine work performed on a self-employed or employed basis for someone else.
Case law has held for decades that such work can amount to a breach of contractual good faith.
This isn't solely a medical question.
It's a question of contractual loyalty.
Compatible with the condition does not automatically mean compatible with the contract
Imagine that someone on sick leave regularly carries out a professional activity for third parties.
The defence may argue: "That didn't make her illness worse."
That may be true.
But it doesn't necessarily settle the case.
There's another question: why is she able to provide services professionally to a third party while her own contract remains suspended due to temporary incapacity?
Conduct can be medically tolerable and, at the same time, disloyal from an employment standpoint.
But not every act of help is work
This doctrine doesn't mean that any gesture made during sick leave automatically turns into clandestine work.
Case law has also rejected dismissals where all that was proven was occasional or insufficiently significant collaboration.
Spending a few minutes at a relative's business isn't the same as continuously carrying out a genuine professional activity.
That's precisely why private investigation becomes so important.
The investigator shouldn't chase only a striking photograph.
They must document facts sufficient to determine the true nature of the activity.
The investigator's question changes: conduct or work?
If we're investigating sport, leisure, everyday tasks, or travel, the goal remains to document what's relevant to the functional limitation, recovery, or fitness for work.
If there are signs of professional activity, the questions change:
Does she regularly go to the same place? At what times? For how many days? What tasks does she perform? Does she serve customers? Does she use professional tools? Does she handle merchandise? Does she give instructions? Does she open or close the establishment? Does the behaviour repeat?
The goal is no longer to photograph activity.
It's to document work.
Regularity matters, even without a magic number
A single occurrence can be ambiguous.
Several sequences make it possible to understand continuity, organization, schedule, tasks, and integration into an activity.
There's no rule that "three days equals work."
But repetition helps distinguish an occasional favour from a professional pattern.
That's why a good investigator doesn't chase only the spectacular image.
They chase the pattern.
The report should describe, not label
It shouldn't casually state that "the subject is working illegally as a cleaner."
What was seen should be described: schedules, addresses, duration, materials, entries, exits, and repetition.
The lawyer will build the conclusion afterward.
The less we editorialize, the harder it will be to dispute our facts.
This doctrine did not originate in 2025
The recent ruling is interesting because it clearly applies a settled doctrine and corrects a first-instance reading focused solely on harm to recovery.
But the so-called "second pathway" wasn't born in 2025.
The TSJ of Catalonia and other courts have for years been reiterating the Supreme Court's case law from July 1990 on harmful activities, fitness for work, and contractual good faith.
The importance of the recent ruling lies in reminding us that this doctrine remains fully alive.
Conclusion
During temporary incapacity, activity and work aren't the same thing.
Not every activity amounts to fraud. Not every activity delays recovery. Not every conduct justifies a dismissal.
But genuine work activity can shift the problem from medicine to contractual good faith.
And that's where private investigation can be decisive, because determining whether someone is genuinely working takes more than a photograph.
It takes observing, repeating, contextualizing, and distinguishing the occasional from the professional.
At Método 3 the rule is simple:
if we want to prove incompatibility, we document the activity. If we want to prove work, we document the pattern.
Truth has a method.