Can your unit commander stop you from ROTC contracting due to coming deployment?

Can they? Yes. Will they? Who knows. Have you had a sit down with your Command Team to discuss this?

If you are asking if they can stop you from signing an ROTC contract? No, they can not. However, you will need to complete an SMP agreement with your ROTC contract. If your unit won't accept you as an SMP cadet, then speak to your state guard's Officer Strength Manager, they will move you into a new unit to be an SMP cadet. Why are you not contracted already? As an MS03, you should be contracted already. Once contracted with ROTC, you become an SMP cadet and are non-deployable.

Need more info are you SMP? Guard or reserves going to school? Need more info to help you, be detailed. Or are you active duty?

I will first caution you on operational security or OPSEC. You have enough information here to give anyone an idea who is deploying and where you are going. Now from your question, I assume you have not signed an ROTC contract yet. Your NG unit commander has to approve your SMP contract so they can decide that you are mission critical for the deployment and not sign the SMP agreement. The State’s officer strength manager though could also have some say if they deem it more important in the long term to gain an officer. However, if you have an opportunity to deploy and know you want to be an officer, do the deployment. You earn education benefits you would not otherwise have.

If he/she doesn't sign your paperwork then yes you will deploy first and when you come back you should be good to go. The only issue I could see with this is timing. If you waited to bring this up right before the deployment then they may see it as you trying to get out of it. Second thing, don't forget it's mission first. If your mission requires that he maintains a certain percentage to deploy then you'll just have to wait. Typically, this is not an overnight thing and your commander should have been tracking if you told them. I'm in ROTC currently and haven't seen a commander do this. Most issues are the result of lack of communication or misunderstanding.