Agree with Sir Humphrey. Most strata committees will use their official stationary responsibly but if it is being misused then you need to adopt a set of rules (there are no relevant laws or codes of conduct in NSW).
The committee can agree to restrict its use to official communications with authorities, or approved communications with residents, following agreement at committee. That should dial it down a little.
The problem may be, however, an over-zealous secretary who could resent being reined in. That’s a whole other issue that may have to be handled diplomatically, especially if there isn’t anyone else prepared to take over the role.