Keep in mind that it is the Owners Corporation that must pursue a breach of by-laws action. So, your building’s strata committee, or a majority of owners voting at a general meeting, must approve taking this action. As the potential miscreant is on the strata committee there are some practical concerns about how to bring this about.
But before you worry about that, there are some preliminary steps to take. There should be a warning given to the miscreant, or more than one, which needs to be documented, and the response considered. This is normally carried out by the strata manager (or strata committee if there’s no manager), and so you need to write/email these to tell them about the possible breach, and to send a warning to the miscreant. It may turn out there is no breach? Have you checked your building’s by-laws to review their wording, to see if the behaviour is an actual breach? Is there a reasonable explanation? And, importantly will a majority of members of the strata committee, or a majority of owners at a general meeting, support taking further action?