Under the Labour Law No. 4857 (Turkey), a principal employer–subcontractor relationship arises when certain tasks related to the production of goods or services in a workplace are assigned to another employer.
This relationship occurs when an employer transfers auxiliary tasks related to production or services, or a specific part of the main work, to another employer due to operational needs and technological reasons requiring specialized expertise. The subcontractor employs workers specifically for this job, and these employees work only at the workplace where the job has been assigned.
Auxiliary work refers to activities that are connected to the production or service process but are not directly part of the core production organization. These tasks continue as long as the main activity continues and remain dependent on it.
Main work, on the other hand, is defined as the core activity that forms the basis of the goods or services produced by the business. A part of the main work may only be assigned to a subcontractor if it requires specialized expertise due to the nature of the work and the needs of the business.

According to the legislation, a subcontractor must complete workplace registration by submitting a written subcontracting agreement made with the principal employer along with the required documents.
The contract must clearly include the following elements:
These requirements are regulated under the Subcontracting Regulation (Turkey).
Once a subcontracting relationship is established, joint liability arises between the principal employer and the subcontractor. This means that both parties may be held responsible for certain legal and financial obligations.
The main risks include:
If the subcontractor fails to pay the social security premiums of its employees, the principal employer may also be held responsible before the Social Security Institution of Turkey
If the subcontractor fails to pay wages, severance pay, notice pay, or other employment-related receivables, employees may also claim these rights directly from the principal employer.
In the event that subcontractor employees experience a work accident or occupational disease, both the subcontractor and the principal employer may be held responsible for compensation claims and other liabilities.
If adequate occupational health and safety measures are not implemented in the workplace, managers or authorized personnel of the principal employer may also face legal responsibility.
Therefore, it is not sufficient to only establish the subcontracting relationship through a written contract; the actual practices in the workplace must also comply with the law.

One of the most common issues encountered during inspections or legal disputes is collusive subcontracting. This occurs when a subcontracting arrangement is formally established but does not reflect the real working relationship.
Situations that may be considered collusive include:
If an inspection determines that the subcontracting relationship is collusive, the subcontracting contract is deemed invalid. In such cases, the workers employed by the subcontractor are considered employees of the principal employer from the very beginning.
As a result:
Employees may also claim retroactive wage differences, social benefits, and other employment-related receivables.
Additionally, if social security notifications were incorrectly submitted, administrative fines may be imposed due to missing or late declarations.