The preventive situations are defined by ERSE:

• Insufficient or invalid installation identification;
• Requests overlay switching supplier;
• Power indicated not standardized or higher than the requested or licensed power;
• Customer data not matched with registered;
• Existence of fraud processes;
• Amounts owed to the supplier of last resort, which has not been contested before the courts or authorities responsible for extrajudicial dispute resolution.

Customers may also be prevented from contracting the supply with a supplier if there are amounts owed to the last resort supplier (CUR), which have not been challenged before courts or entities with the power to resolve judicial conflicts.