Australia's two major supermarkets, Coles and Woolworths, both have a limit of two tins per customer in place.

Retailers introduced the restrictions last year after concerns baby formula was being purchased and on-sold for profit overseas, particularly in China, causing supply shortages for Australian families.

Tegan Shirbin, a new mum to twins, said she has had great difficulty feeding her 11 week old babies, Octavia and Troy, who have to be solely formula-fed for health reasons.

The Googong mother said in just the past few weeks she had five arguments with supermarket staff who have tried to stop her from purchasing more than two tins of formula.

Ms Shirbin said her twins consume two tins in about four days and supermarkets needed to realise parents of multiples needed more than the limited amount of formula.

"I have to take what I can get because I don't know when I'll be able to get [to the shops] again," Ms Shirbin said.

"I have double the babies, I should be able to get double the formula."

Australian Multiple Birth Association chairperson Ashlee Tenberge said the organisation had heard similar stories from around the country of parents with multiples having to justify at the checkout why they need more formula.

Ms Tenberge said the restrictions should take into account the logistical issues of having multiples such as greater difficulty for parents to get to the shops and the sheer volume of formula multiple babies go through.

"The retailers don't seem to understand these issues," Ms Tenberge said.

Ms Shirbin said she has had to resort to desperate measures to ensure her babies are fed properly and has called in her parents and in-laws to purchase formula for her.

"I'm really stuck with what I can do," Ms Shirbin said.

Both Ms Shirbin and Ms Tenberge said they understood the reasons for the restrictions.

Ms Shirbin said it was more difficult when she regularly couldn't find formula on supermarket shelves. But, she said all she was asking for was greater understanding.

She said it was a "ridiculous" situation, to stand at a counter holding twins and having to justify buying extra formula tins.

Ms Tenberge's advice to parents facing the situation was to make contact with their local supermarket earlier than in the checkout line when it might be too late.

She said if they could get to know their local store manager they may be able to organise an exemption due to their increased need.

A spokeswoman for Coles echoed this advice and encouraged parents to speak to their local store manager if they need more than two tins to feed their children.

"Coles is committed to ensuring that our customers with a genuine need for infant formula have access to this product," she said.

A Woolworths spokesman said the company would look into ways to increase supply of baby formula.

"While we know the vast majority of customers only buy what they need for their family, our teams do work hard to uphold the two tin formula limit in our stores," he said.

A small number of NSW Coles supermarkets will be stocking certain brands of formula behind the counter but this will not spread more broadly and will not be introduced in Woolworths.