It isn't absolutely necessary, but having an attorney send the letter will amplify the force of your demands. Also, as mentioned below, if you decide to contact

It isn't absolutely necessary, but having an attorney send the letter will amplify the force of your demands. Also, as mentioned below, if you decide to contact them yourselves, you may unknowingly produce evidence that can later be used against you, or you may lose your head and make a threat you shouldn't make. It shouldn't take an attorney more than one billable hour. Having an attorney send the letter may save you money, if you consider how long it would take you to research and write, depending on at what rate you value your time. One thing, and you probably already know this, when you say "ask them to change their direction," don't expect to succeed in keeping them from competing with you. They have a right to express the idea that you are expressing, they just have to write their own copy and markup to legally do so.