Wiener Linien, Vienna's public transport operator, sets out its own official rule directly on its site: any dog not travelling in a closed container must wear a muzzle and be on a leash — a Maulkorb- und Leinenpflicht — while using the tram, U-Bahn or bus network. The detail that genuinely surprises visiting owners is where the rule starts: for the U-Bahn specifically, Wiener Linien's own wording is that the muzzle and leash 'müssen angelegt werden, bevor die Station betreten wird' — they must be fitted before entering the station itself, including the elevators down to the platform, not merely before boarding the train.

For trams and buses, the threshold is less strict: the muzzle and leash need to be on before boarding, with the stop itself not covered by the rule. Wiener Linien sets no specific numeric size or breed threshold for which dogs need a muzzle — the page refers generally to 'kleine Hunde' (small dogs) as a category that can skip it by travelling in a closed container instead, since a small dog on the floor risks being overlooked in a crowd.

On fares, a small dog in a closed container travels free, as does a certified assistance dog with a valid entry in its owner's Behindertenpass. An ordinary dog needing its own ticket requires a reduced single '1 Fahrt WIEN' fare for one trip, or a full-price Zeitkarte (such as a 7- or 31-day pass) for multiple journeys; an annual pass holder can bring one dog along at no extra charge.