The PnP TaxonomyPicker reusable control doesn’t have a property to let you mark the input control as a required field on a form, but fortunately, this can be easily addressed.
If you have used the PnP TaxonomyPicker reusable control before, you may have noticed that it doesn’t have a property to make it required, nor does it have a property that lets you add a custom CSS class to it. The problem is that your other required input controls on the form will have a ‘*’ after the label, but not the TaxonomyPicker controls.
But there is a very simple way to solve this because the control also has a Label control, so we can mimic the styles from other Office UI Fabric input controls.
Simply create a new CSS rule that includes a class and targets a label as a child item
.required label::after {
content: " *";
color: rgb(168, 0, 0);
padding-right: 12px;
}
Now add a new element wrapping the TaxonomyPicker (a div, for example)
![TaxonomyPickerCode](https://web365devp-b3bce47612e4cb5767ba-endpoint.azureedge.net/wp-content/uploads/2018/08/taxonomypickercode.png)
And now your TaxonomyPicker field will look exactly like the other required fields.
![RequiredField](https://m365-dev.com/wp-content/uploads/2018/08/requiredfield.png)
All you have to do now is implement validation.
Setting the field as required may be an option in the near future, but until then, this is a very simple workaround
Are you also using the PnP PeoplePicker control? Then you may want to check this blog post.