Hello Dannii
If the walkway is only one metre wide and is common property, then the pot-plants unfortunately represent a tripping hazard: hence this has become a WHS issue and the OC is liable if anything happens, and the EC (particularly those who voted in favour of keeping the plants) could be personally liable under the revised laws. There are also laws about ability to egress in a fire (I assume this walkway is the only way in/out) as well Australian standards about the minimum safe width of a passageway.
Additionally, most bylaws have provisions about not storing items on common property/and or blocking access. It would seem these plants are in breach of both and can be dealt with via a notice to comply.
But, the easiest way to getting others around to a different point of view is to make it their problem from their point of view: explain to them that the OC will be liable for any injuries that occur as a result; explain that insurance premiums go up and that they may personally cop a fine or jail time or both.
If those don’t work (it sounds like your SM wouldn’t send a notice letter anyway given he advised you to vote amongst yourselves), use your EC position to raise the item at the next AGM, present your argument and get the OC to vote for it.
Good luck