Accepting Freelance Jobs while working under TN visa

Hello,
I've been working in the US for 2 years under a TN visa as a 'Computer Systems Analyst'. My friend's company wants to contract me for a small freelance job. Am I allowed to accept payment? They are asking me to fill out a W-9 form for tax purposes? Will this jeopardize my current situation in the US? Should I ask them to sponsor me so I can work under two TN visas?

This violates your TN status even if you are not getting paid.

Yes, getting a second TN is the way to go.

multiple TNs is the only way to do this. manner of payment or non-payment does not matter. It's work requiring another tN.