A construction site operating on Sundays with workers who have never been officially registered, an employee paid a “fixed fee” who has never signed a contract, a competitor who undercuts prices because they don’t pay social security contributions, and the infamous “extras” in the restaurant industry.
In 2024, URSSAF recovered a record 1.6 billion euros in unpaid taxes related to undeclared work—about 34% more than in 2023 and double the amount from 2022. Undeclared work is thriving.
Faced with the difficulty of gathering concrete evidence, both companies and employees can hire a private investigator to document a case of undeclared work.
What is hidden work?
Hidden work refers to working or making someone work without complying with certain legal obligations, particularly those relating to declaring the activity or the employee.
It consists of keeping a professional activity “under the official radar,” outside legal obligations. This deprives the State of contributions and workers of their rights.
Hidden work is often confused with social fraud and the employment of foreign workers without authorization.
In practice, hidden work manifests mainly through:
- Concealment of activity (Art. L. 8221‑3): A person carries out a lucrative economic activity without registering or declaring their activity/turnover.
This may include total or partial concealment after a refusal of registration or continuation of activity after deregistration for failure to declare for two consecutive years. This is the “ghost entrepreneur.” - Concealment of salaried employment (Art. L. 8221‑5): The employer does not file the mandatory hiring declaration, does not issue payslips, or under‑declares actual working hours. This is the “invisible employee,” paid partially off the books.
Fraud requires intentional evasion, distinguishing hidden work from a simple administrative error.
This offense has victims: it deprives employees of rights, society of contributions, and distorts competition between businesses.
What are the sanctions for undeclared work?
Undeclared work exposes its perpetrator to criminal, administrative, civil, and social sanctions:
Criminal sanctions
Article L. 8224‑1 provides up to 3 years of imprisonment and €45,000 fine for individuals.
For legal entities: €225,000 fine, multiplied penalties, and complementary sanctions such as administrative closure, prohibition from operating, or publication of the decision.
Administrative sanctions
The administration may withdraw exemptions or public aid, exclude the employer from certain benefits for a set period, or refuse social advantages linked to employment.
In practice, controls may also lead to loss of fiscal or social advantages and consequences with URSSAF.
Civil and social sanctions
The employee may obtain specific compensation if hidden work is established, especially upon termination of employment.
The employer faces reassessment of unpaid social contributions, with penalties and surcharges.
Who has an interest in proving it, and why?
The employee
This is the most common case. They may work without a contract or payslip, or see their hours systematically under‑declared. When the employment relationship ends, they must gather evidence proving the reality of their work.
If they demonstrate the existence of genuine salaried employment, they may obtain judicial recognition (requalification).
They can claim unpaid wages, overtime, and especially the fixed six‑month salary compensation under Article L. 8223‑1 of the Labour Code, in addition to termination indemnities.
But the burden of proof lies with them. They must establish:
- Actual presence at the workplace
- Work‑related movements
- Tasks performed
- Any harm suffered
This is precisely what a private investigator can document.
The company
A competitor using undeclared labour avoids social contributions and labour law rules, allowing artificially low prices.
For honest companies, market loss is direct and sometimes vital.
The law provides a remedy: unfair competition action, allowing damages or civil party status in criminal proceedings.
Individuals and insurers
Individuals employing domestic workers may face fraud or be exposed if they fail to regularize the situation.
Hidden work and insurance fraud
An insurer may suspect fraud when an insured person receives benefits while continuing professional activity (sick leave, disability, social benefits).
The activity may be regular or occasional, declared or undeclared. This may contradict statements made to the insurer, who must gather objective evidence.
The private investigator verifies the reality of the professional activity:
- Observing movements and behaviour in public
- Identifying schedules and frequency
- Determining conditions of activity
Their report compiles objective findings, respecting proportionality and the rights of the monitored person.
What evidence can demonstrate hidden work?
Proving hidden work requires gathering objective elements about the actual activity:
- Documents, invoices, exchanges, testimonies
- Online professional ads or publications
- Concordant elements: schedules, locations, regularity
The private investigator complements these with field observations:
- Repeated presence at the workplace
- Schedules, movements, tasks performed
- Use of professional vehicles, deliveries
- Presence of clients
The investigator compiles these findings in a dated, detailed report, without exceeding the scope of observed facts.
This transforms suspicions into material, verifiable evidence.
How can a private investigator concretely prove hidden work?
A private investigator is useful when there are serious suspicions but insufficient objective evidence.
They observe and document hidden activity, identifying who works, when, and for whom.
Typical investigations concern activity during sick leave, holidays, or in violation of exclusivity or non‑competition clauses.
Methods include:
- Surveillance and tailing in public areas
- Material observations
- Collection of oral or written testimonies
- Open‑source intelligence (OSINT)
- Verification of actual schedules and activities
- Preparation of a bailiff’s report
Their intervention is limited by proportionality.
They cannot access protected files, bank accounts, or confidential data.
Crossing these limits exposes them to criminal sanctions and weakens the evidence. Our team is ready to guide you and materialize your suspicions and doubts to defend your rights and interests. Contact us for a professional guide.
FAQ
Is a private investigator’s report admissible in court?
Yes, and its value has even increased.
Since the Court of Cassation’s ruling (Ass. plén., 22 Dec. 2023, n° 20‑20.648), evidence obtained without someone’s knowledge is no longer automatically excluded.
The judge balances the right to evidence with privacy rights.
A report is admissible if indispensable and proportionate.
Hidden work, social fraud, employment of foreign workers without authorization: is it the same?
No.
- Hidden work: undeclared activity or employment
- Social fraud: undue benefits or contribution evasion
- Unauthorized foreign employment: employing someone without work authorization
A situation may combine several offenses, but each has its own rules.
Can an employee paid “off the books” be sanctioned?
Generally no: the employee is considered a victim.
They retain their rights, including the six‑month compensation.
However, if they knowingly receive benefits (unemployment, sick leave, RSA) while working, they risk prosecution and repayment.
How long do you have to act?
- Criminal: 6‑year limitation period
- Labour court: shorter deadlines depending on the claim
Acting early makes evidence easier to gather.
What can a private investigator provide that I cannot?
A CNAPS‑licensed investigator conducts surveillance, collects testimonies, and drafts a dated, detailed report admissible in court.
They materialize facts that an individual could not establish alone without time or legal risk.
