[jQuery] Check to make sure checkbox is checked using validator

[flycast]

My code:
<p>
<span class="required">Do you agree to the terms above? <br></span>
<label><input type="radio" class="radioButton" name="emp_termsAgreed"
value="Yes">Yes</label>
<label><input type="radio" class="radioButton" name="emp_termsAgreed"
value="No">No</label>
</p>

I want to require that the checkbox with the value of "Yes" is checked
before the form will submit.
How is this done?