Tasmanian Logistics Committee chairman Brett Charlton said he was currently contacting shipping lines to find out what container numbers they would have available during the peak harvest season, which begins in December.

He said Tasmanian exporters would be competing with a bumper harvest predicted for the mainland.

"There are very full ships coming into Australia and you have to be concerned about which shipping lines are going to reposition empty reefers (containers) here for the export shipping markets, when they are moving high-paying, full-retail cargoes to Asia" Mr Charlton said.

"In the past you would have had shipping lines reposition empty reefer lines here in preparation for the export season,.

"My concern is the lines won't have much motivation to reposition the containers, at their cost, down here, when they are already getting high value containers on other routes"

Mr Charlton said coronavirus had not affected intrastate trades through Toll Holdings, the TT Line and SeaRoad.

"By and large, between here and the mainland, it's been quite good - but internationally it's a different story."

While the federal government's International Freight Assistance Mechanism (IFAM) was helping, particularly with seafood exports, there were now also concerns about industrial action at Port Botany, NSW.

"While international shipping hasn't been too bad, we are certainly seeing some issues now and we are concerned about the future," he said.

"Tasmania always has a lull in its trade output over the winter months but it will be tested over the summer months"

The Maritime Union of Australia (MUA) currently has an industrial campaign running in Sydney, causing ships to be diverted.

The union has been in talks with three stevedoring companies for a six per cent wage rise, spread over four years.

Mr Charlton said schedules were "quite chaotic" at the moment.

"The action has a butterfly wing effect, in that the MSC service from Bell Bay, runs via Sydney, so we have seen omissions in sailings and exports go to Noumea, before going back to Brisbane, and then being transhipped.

"We're having ships bypassing Sydney and discharging their cargo in Melbourne.

"My concerns today are what it's going to look like when our agricultural season kicks in down here."

Further concerns were due to a sharp jump in freight prices.

"Last year you could get a container from Shanghai to the eastern seaboard for about $US300 - now they are going to be US $1800.

"From a shipping point of view, you have full capacity and you have higher than ever freight prices."

Tasmanian Agricultural Productivity Group executive officer Terry Brien said the industrial action in Sydney was "not helpful".

"We are coming up to a busier and busier time as the harvest gets into full swing," Mr Brien said.

"Any delays in fright across Bass Strait will have really adverse affect on our companies.

"We do still have companies that are exporting - whether they do get caught up with the (union dispute) we will have to see.

"All we can do at our end is harvest, clean and pack in good order, and hopefully the supply line holds up for us."

But Harvest Moon, Forth, co-owner Mark Kable said his greater concern was over labour shortages.

"There are certain times of the year when it does get tight, leading up to Christmas and again around Easter, but I think we are pretty well serviced at the moment," Mr Kable said.

"We predominantly used Fresh Freight Tasmania, which uses TT Line, and we back it up with SeaRoad."

While concerned with the rise of freight costs, he said Harvest Moon's greatest challenges would be securing labour while the border closures are in place.

Tasmania's border closed from August 20, with all non-essential travellers, including Tasmanian and non-Tasmanian residents required to have prior approval before entering the state.

"Our biggest worry is labour, not freight," he said.

"We need to open the border up, full stop. We need to get that border open, as soon as possible.

"That would remove a lot of headache and a lot of extra work with on-farm quarantine."

"I'm hopeful now that SA has moved, other states will follow."

Harvest Moon process carrots, onions, broccoli, cabbages, beans and spinach.