Identify the unfair aspect with respect to the sentence extracted from an online Terms of Service:
```
you may be required to be a registered user in order to purchase some services . 

```
. OPTIONS: ['Unilateral termination' 'Choice of law' 'None' 'Limitation of liability'
 'Content removal' 'Arbitration' 'Contract by using' 'Jurisdiction'
 'Unilateral change'].