What do you do when a soldier refuses to listen to your directions?

Its not only a question of uniform standards, its insubordination. Counseling and recommendation for UCMJ is called for. If not addressed the negative behavior will continue and more Soldiers will be emboldened to replicate the behavior and the problem will become worse as you lose credibility and authority as a NCO.

This is easy it actually falls under Ar 670-1 uniform policy, due to the army policy on umiformity. You can find authorized eyewhere there. This falls under the same guise as jungleboots in formation, without the commanders expressed permission in a policy letter it violates the uniformity rules of the Army unless the eyewhere is prescribed.

UCMJ Article 92
Failure to obey a lawful order.

first ask the soldier for the glasses, if he/she refuses AGAIN, remove them from said soldier's head. IF the soldier attempts to block you (NCO) BLOCK HIM/HER...it should NOT have to get this far...IF it does, it tells me an awful lot about what has become of the army....

that's the problem with the military today, too much disrespect, they disobey orders ...what do you think is gonna happen if they go to combat. the enemy isn't gonna give them a stress card or sugar coat anything for them. To much political BS.

In my day a sailor refusing to follow a lawful order found himself in deep shit. I would arrange for him to do the worst jobs I could find along with curtailing his liberty. If that did work he would eventually find himself at Non judicial punishment.

Questions..
Is he/she assigned to you?
on the initial/reception counseling specifically comments about abiding by AR670-1 and unit Standards?
any history of other infractions? << any written trail?

You document the infraction of the eyewear in formation for refusing an order you immediately remove them from formation take directly to First sergeant and I would highly recommend article 15 action failure to obey an order and conduct unbecoming. You can’t allow for any reason for this not to go unpunished. In the field you have to be able to trust that your orders will be followed and if you don’t have confidants in the solder then it will affect your decisions and that my friend is when people die.

You dismiss the soldier in question from formation the first time and have them do shit duties, bring it up with your immediate Chain of Command as a paper trail and go about the rest of your day. UCMJ is not required for this. What they need is a lot of hard work digging holes and filling them, useless tasks while making it clear that if they are not going to conform to your directive then they will get the worst, dirtiest, degrading jobs you can find for them. Make it clear in your reports why you are doing this so you are not seen as discriminating. You are doing this as a lesson and make that clear, with no bias. Men and women who do not conform like this tend to look for excuses to support their actions. When in doubt ask your fellow SGTs..... but UCMJ is not to be used for minor things like this. I used to have people like this clean ditches with no equipment and then I would inspect those ditches requiring them to be clean.

When a soldier disobeys a lawful order UCMJ action should be taken. There is a difference between slowly complying to an order , than outright refusing one. In which an official counseling is most likely to take place .