Because that will be their ROE. It will also be Russian ROE.
Only a fool commander would order a large battalion to fire on the Russian Army in Ukraine. Only a fool Russian commander would order fire on a thousand American troops unless their goal was existential war.
Frankly, I am unfamiliar with the acronym. (ROI is return on investment; but I have never before heard of ROE--unless it is followed by "v. Wade.")
Only a fool commander would order a large battalion to fire on the Russian Army in Ukraine. Only a fool Russian commander would order fire on a thousand American troops unless their goal was existential war.
I really do not expect either to happen.
But if Russian troops were to attempt to "escort" American troops anywhere, the certain upshot would be open hostilities. Of that, I feel certain.