Guidelines like what is allowed within your organization? Does your organization have policies or guidelines around what you are allowed to share internally related to these or other types of events? It looks like you work for a government agency. My guess is that there are policies in place about what you can and cannot discuss/promote. I would start there. For example, at my previous company we didn't allow any craigslist type groups because within the organization selling personal stuff was against corporate policies. Additionally, unless the charity was approved by the company, you could not promote personal charities. Religious organizations/discussions were also against corporate policy.