The employer can demand the employee to stop using the copyrighted recipe and might have grounds for termination since employees are prohibited from disclosing proprietary information and trade secrets.
If an employee is using an employer's copyrighted recipe for personal gain and in violation of company policies regarding proprietary information, the employer may lawfully demand the employee to cease the activity and could potentially terminate their employment.
This is because trade secrets, such as secret recipes or methods not covered by patent law, are protected under the broader sphere of intellectual property rights and must not be disclosed or used without authorization. The size of the employee's business or the existence of a collective bargaining agreement does not necessarily protect against violation of trade secret laws.