The purpose of work must be to uplift both others and yourself. (Here I am using the word ethical in the context of serving the highest good of all): If building your own hurts your employer’s business, it is not ethical. If your employer’s business prevents you from growing, that business is not ethical. If both the employer and you were ‘ethical’, you will treat each other as brothers and sisters. You support your employers, they support you. You take full responsibility for their well being, and they for yours. It is not that you step over their free-will, but still you feel responsible for their well-being. Ideally: Full respect of the other’s free will and taking full responsibility for their well-being and your well-being and the well being of all beings in existence.
When you act this way, the employer may agree or not. It doesn’t matter if they agree or not. If they don’t agree, you will still be preserving the highest integrity and can decide the next action. If they agree, great, you will be a good team working with a similar sense of brotherhood. Moving with the highest good of all at heart and mind is the wisest action. It will give the greatest happiness, peace of mind and inner freedom of creativity while you will need to trust the core of your being as you expand the horizons of your awareness.
You must also check the agreement you made between you and the employer when you began working with them. If that agreement disallows you to work in your own business, then it will be unethical to work this way. If you update the agreement between you and the employer and there is mutual consent, then there is no problem. Openness is very important here, unless you are already sure that you are doing the best for yourself and the employer and they would not be able to understand your good intentions. Yet, if you can’t be open with your employer, why would you keep working for them? You must take responsibility for the whole picture, for your entire life experience. Actually, it is hard for me to see and warn about all the possibilities here in writing. I tried to reflect on them some more in this paragraph. That is why you must take full responsibility in your situation and go with the guidance of your conscience.