Coal has traditionally been tested for ash and sulphur levels, but Chinese customs, who preside over the second largest market for Australian coal, have recently started testing coal arrivals for fluorine and phosphorus as well.

The new testing regime, which is at odds with the internationally recognised testing system ISO, forced one shipment carrying 70,000 tonnes of coal from Newcastle in New South Wales to be sent back to Australia in March, and that shipment is understood to belong to Anglo American.

Anglo American declined to comment when asked if some of its coal had been rejected by Chinese ports.

Other miners were less secretive with BHP Billiton and Glencore confirming that none of their shipments had been rejected.

"BHP Billiton analyses its coals before shipment using certified international standards and all are capable of meeting the regulation. None of our shipments to China have been rejected on this basis," said a spokeswoman.

"We are working as an industry to identify if any process improvements can be made to assist all parties."

While the number of Australian ships understood to be turned around remains at the one Anglo American vessel, industry speculation suggests there have been more, with producers in South Africa and Canada also affected.

Australian producers believe the trend is motivated by a desire to protect struggling Chinese coal miners, rather than protect the environment, and ICIS China energy analyst Deng Shun agreed.

"I think the environment issue is a secondary reason, the most important issue is that China's coal market over-supply is too serious," he said.

"A lot of Chinese coal suppliers, because of this over-supply, have seen their prices drop and suffered serious losses. Many companies have incurred such serious losses that they can't pay employee wages."

But the clearest impact of the new testing regime lies in the volumes of coal bypassing China for other markets.

Chinese imports of coal in the first five months of 2015 were 38.2 per cent lower than the first five months of 2014.

The import slump was particularly stark during the month of May, when China imported 37.6 per cent less Australian coal compared to the same month in 2014, and 25.6 per cent less than in April.

Those reductions came despite Australian coking coal production rising over the past 12 months and Australian thermal coal production falling by less than 1 per cent.

Minerals Council spokesman Greg Evans said Australian miners were concerned that Chinese coal producers may not be subject to the same tests, and were frustrated by the extra costs and delays that came with the tests.

"The main problems relate to the variability in the testing regime, inadequate allowance for commercial remedies and the delays it is subjecting shipping to, there is no doubt each of these factors adds to cost and increases risk," he said.

Mr Deng said some Australian miners were now sending samples of their coal to China ahead of time in a bid to make sure their cargoes would not be turned-back at the border.

"You can say that ISO is the international standard but the fact is China is [one of] the biggest buyers. So there's not much you can do," said Mr Deng.

"If Australia wants to sell coal in China, at the moment, they'll just have to adhere to the local rules."

Mr Evans said the council was working with the Australian government to broker a resolution to the testing.

"Australia is looking for a practical and speedy resolution and is working with our government to that end. It would seem sensible for both governments to agree to cease or suspend the operation of the quality regime and now take stock, this could allow for possible solutions such as conducting internationally accredited testing in Australia prior to shipments taking place," he said.

– with Peter Ker

This article first published in the Sydney Morning Herald