Postal start-up Sendle is taking on Australia Post, writing a submission to the Australian Competition and Consumer Commission's letter pricing inquiry and starting a Change.org petition to get the business to allow other courier companies to deliver to PO boxes. 
Its push is supported by Fastway Couriers and the Supply Chain and Logistics Association of Australia, which believe Australia Post is abusing its position.
Sendle chief executive James Chin Moody said the Australia Post had "a license to a monopoly".
"It hurts consumers. I can't find anywhere on the Australia Post website that tells consumers only Australia Post can deliver to PO Boxes," he said.
Sendle's Change.org petition has already attracted 6831 signatures of support. 
"You can see the traction the Change.org petition has received, as well as the comments on the petition, on our social channels and on other online forums. Australian businesses are crying out for this to change," Mr Chin Moody said.
"What's worse is the limitation is not communicated to PO Box customers. It's similar to Telstra saying you can only call a Telstra landline from a Telstra mobile."
In a statement a spokesperson for Australia Post said PO Boxes were treated as a commercial product and that commercial arrangements could be struck with other freight companies but no information on pricing was readily available online. 
"PO Boxes are part of the Australia Post delivery network. Australia Post delivers some other carriers' articles to PO Boxes under commercial agreements. Australia Post is happy to talk to Sendle about forming a commercial arrangement to provide the same services," the spokesman said.
Fastway Couriers chief executive Richard Thame said it's become a bigger issue since consumers have started online shopping and don't know which company will deliver their goods.
"If they're paying for the PO Box service they should be able to take deliveries by other companies," he said.