Dylan-Lee Polanco is 23 weeks' pregnant and was expected to fly home to Australia with her husband, Emilio, on Wednesday.

But the couple, who will live with Ms Polanco's mother in Ballan when they return, were bumped off their flight three weeks ago after the federal government halved international passenger arrivals due to the threat of COVID-19's Delta strain.

The Polanco's paid $2500 each for their airline ticket and it is feared people who can afford to pay tens of thousands of dollars for their one-way ticket to Australia are being prioritised.

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International airline tickets skyrocketed when arrival caps halved on July 14 and airlines have been warned against gouging.

Ms Polanco is desperate to get home on her rescheduled flight on September 11 because it is unsafe for women who are 28 weeks' pregnant to fly.

Her family, including her sister Jade Lourey who lives in Ballarat, are worried Ms Polanco may have to give birth in the US.

Ms Lourey said her 27-year-old sister was having a difficult pregnancy and she had planned to raise her family in the Ballarat area where she had family support.

"Dylan is really anxious. Deep down she is worried she can't make it home. She wants to have her baby at home," Ms Lourey said.

"I am worried. After she got bumped off the first flight, what's to say it won't happen again?

"We just have to hope she can make it home because if she can't, she may not be allowed to fly home."

Ms Lourey said Ms Polanco belonged to a really close family and seeing her stuck overseas was devastating.

While the Polancos are rushing to get home, their pet dog - a cocker spaniel cross dachshund - will fly home this week without them and stay at Mr Polanco's parents' Bacchus Marsh house.

The Polanco's moved to the US about seven years ago when Mr Polanco's father, who lives in South Carolina, needed a visa sponsor.

After getting married in 2019 in Australia, they returned to the US to tie up some loose ends but their plans to move back last year changed due to the COVID-19 pandemic.

Ms Lourey said knowing they had a flight booked to return home, her sister and brother-in-law resigned from their jobs, ended their lease on their apartment and got their COVID-19 vaccinations.

But she said three weeks before their scheduled flight, the airline informed them they had been bumped off their flight.

Ms Lourey said the airline knew her sister was pregnant. She said the family was doing everything they could to try and get Ms Polanco and her husband home.

"I worry about her every day," she said.

The Polancos have registered with the Department of Foreign Affairs and Trade as being stuck overseas and wanting to return home, however they have not heard anything from the department.

Mr Polanco, who has an American citizenship, is receiving government support while Ms Polanco - a graphic designer - is unemployed, which makes them ineligible for health insurance.

The couple were lucky they had a friend who gave up her apartment for them to live in until they can get home. They are living under the food stamps program.

Ms Lourey said the Polancos had to sell everything and the coming months would be financially difficult for them.

She said friends in the Ballarat and Ballan area had been very generous and donated baby items for the couple.

Ms Lourey said her sister and brother-in-law would need to quarantine at a medical facility when they arrived in Sydney, which would cost them $3500, and further quarantine in Melbourne was likely.

Ms Polanco is due to give birth in December.

Australia's limit on international arrivals was cut from 6000 to 3000 passengers a week from July 14 due to the risks posed by the Delta strain of COVID-19.

There are about 34,000 Australians registered with the Department of Foreign Affairs and Trade as being stuck overseas and wanting to come home.

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