A Melbourne pensioner was left mortified after being told she could not pay for part of her groceries using $1 coins.

The 82-year-old woman, known only as Maria, and her daughter, Helen Garvey, were shopping at Coles at The Glen in Melbourne on Friday and were left dumbfounded when they were informed it was illegal to use $1 coins to pay for more than $20 worth of their shopping.

The duo had purchased $130 worth of groceries and tried to pay $100 in notes and $30 in $1 coins. The cashier accepted the payment but told them this would not be the case in future, according to Helen's post on the Coles Facebook page.

Helen called the experience "embarrassing" and "disappointing", subsequently questioning why there were no signs informing customers of the policy.

“My mother and I were quite embarrassed and my question is when has there been a law to what money is accepted at Coles ????," she wrote.

“This is awful my mother is a pensioner and a widow and doesn’t have an EFTPOS card as she is quite beyond technology.

“This is really disappointing and now she feels embarrassed to shop there again,” she added.

“Is 30 dollars in gold coins worth less than a twenty and a ten. And if this is common practise I suggest you have signage so that others won’t feel like they are second-class citizens.”

Her post has since garnered thousands of reactions, including more than 7,000 comments.

Responding to the post on Facebook, Coles said: “We’re disappointed to hear that you had a poor experience at our Glen Waverley store, we adhere to the RBA Legal Tender.”

According to the Reserve Bank’s website, coins are legal tender not exceeding 10 times the face value of $1 or $2 coins. For 5c, 10c, 20c and 50c there is a limit of $5.