A third option is to send an e-mail message. Most congressional websites have a link for sending electronic messages using a web form. Make sure to fully explain your concern in non-technical terms, and include a way that they can contact you for more information.
Mail from constituents is almost always answered, even if they disagree with you or cannot do what you are asking. However, sometimes the staff who read the e-mail send the wrong response, i.e., the message thanks you for supporting legislation that in fact you oppose. If that happens, reply to the message or send a new message letting them know that they misunderstood your position. You certainly don’t want your opposition to be recorded as support!