I would like to confirm that communicating outside of Upwork before an official contract is formed is in violation of our TOS. However, if the client is new you can also politely remind them about our TOS. Feel free to share the job post URL or the client name with me via PM (click on my name) and our team will investigate this further. Thank you.
Rest assured, your account will not be affected in any way. Regarding your communication, feel free to continue communicating with your client on Upwork at any time. Thank you.
I'd like to reinforce something Goran said.
I think there are actually many people (the new ones, at least) that don't know about the fact that you can't comunicate outside of Upwork prior to a contract. So, please, don't think they're trying to approach you like that on purpose, with some other mischievous goal in mind. Just clarify the rules to them.