Have a look at your Strata Plan By-laws. He’s quite clearly in breach of two by-laws if he had done this in our strata scheme. He’s deposited material on common property without permission, and he’s also caused obstruction to anyone else using common property. Consult your Strata Manager about issuing a Notice to Comply with a By-law, depending on his delegation he may be able to do this directly, or it may require an Executive Committee resolution.
The Notice must be served on the offending resident, if no action is taken within the period stipulated on the notice then an application may be made to NCAT to impose a fine for that breach and any subsequent breaches. You have one year after the service to request enforcement.
Refer also to what Whale said a couple of posts back on this topic.