Malcolm Turnbull's recent decree that Cabinet ministers have to resist their urges when it comes to their colleagues raises a question: can an employer impose an office sex ban?
First, there is no law that prevents, or gives employers the power to prevent, consensual nooky between co-workers.
The legitimacy of a staff sex ban would come down to whether it's a lawful and reasonable direction. In most workplace environments, it won't be. While the PM may be able to get away with it because, well, he's the PM, there's little basis for an employer to interfere with the private lives of staff, even if it involves two employees enjoying some adult naptime.
That said, employers can certainly manage the potential repercussions of an office romance leaking into the workplace. Issues such as conflicts of interest like promoting your bed-mate to a highly paid position (ahem, Barnaby), and appropriate workplace behaviour need to be addressed if problems arise. Employers still have a right to make sure their workplace is harmonious and are entitled to manage the fallout from staff liaisons. And if the consensual nature of the relationship goes out the window, including after a breakup, any bullying or harassment (or worse) will need to be dealt with swiftly.
Otherwise, as long as staff are getting on with their work, they can get it on with each other.