Australia Post has hit back at the internet giants Amazon and eBay, saying the Turnbull government’s plan to impose the GST on all online purchases is a good one.

It says the government’s proposed GST collection method – called a “vendor model”, which would require websites such as Amazon and eBay to collect GST for the commonwealth from goods bought online from overseas – is the most efficient way to impose the tax.

It has warned Australia Post shouldn’t collect the tax, despite the pleas of Amazon and eBay, because it would render its parcels business “unviable”.

It says it supports the Turnbull government’s proposed GST plan but hopes it will be imposed a year later than stipulated. The Senate standing committee on economics will hold a public hearing on the bill on Friday.

The treasurer, Scott Morrison, is pushing ahead with plans to abolish the GST concession for low-value goods bought online from overseas.

At the moment, imports of goods worth less than $1,000 are GST-free – including clothing, books, electronic devices and sports equipment.

The government wants to scrap the concession to “level the playing field” for local bricks-and-mortar stores but it wants online giants such as Amazon and eBay to collect GST for the commonwealth using a vendor model.

A vendor model would require that, where Australian consumers have bought products online from offshore suppliers, the responsibility for collecting GST would lie with the seller, the electronic distribution platform or the re-deliverer, depending on the nature of the transaction.

Amazon has attacked the government’s plan, saying it is so poorly designed it will create an “inherent disincentive” to comply.

It said the government should instead use a so-called “logistics model” to collect GST on online purchases, requiring Australia Post (and express carriers and freight forwarders) to collect GST instead.

“Logistics providers already have infrastructure in place to collect information on goods coming into Australia and have well-established processes for GST collection for goods valued at more than $1,000,” it says in a submission.

It also wondered why the government had provided no rationale for ignoring a recommendation from a previous government taskforce to use a logistics model to collect GST.

Australia Post has warned that, if the government adopted Amazon’s suggestion, it would be “adversely impacted” by the extra administrative complexity caused by the imposition of additional revenue collection.

“Any proposal involving collection of GST under a model that requires collection at the border is likely to render Australia Post mail and parcels business unviable in the current market of continuing and significant decline in mail volumes that have put severe strain on the financial position of the corporation,” its submission says.

It argues any changes to the border process must expedite clearance, rather than hinder it, given 59m items are now being cleared through international mail each year.

It says if Australia Post was forced to collect GST on items arriving from overseas, it would cost the federal government roughly $900m a year – vastly exceeding the $300m revenue the GST could be expected to raise.

“However, the ‘vendor’ model as proposed in Treasury Laws Amendment (GST Low Value Goods) Bill 2017 places relatively less burden on the Australia Post infrastructure, processing times and its costs of doing business,” its submission says.

Gary Elphick, the chief executive of Sydney-based company Disrupt Sports, has said the government’s proposed model shows a “fundamental” lack of understanding about how online markets work.