In its statement, a2 Milk said it had become aware of information that may require the company to revise its previously issued earnings guidance to the market.
"We are requesting a trading halt to provide us with additional time to properly consider the current information and to consider new information as it becomes available, and inform the market," a2 Milk said.
At November's annual meeting, the company said it still expects group revenue for the first half of $725 million to $775m, down from $805.3m in the previous corresponding half.
Group revenue for 2021 was expected to come to $1.8 billion to $1.90b, up from $1.73b in the 2020 financial year.
The 2021 year's Ebitda margin was forecast to be in the order of 31 per cent.
"However, due to the volatility arising from Covid-19, and the difficulties this presents with forecasting, naturally there is uncertainty to this forecast," the company said at the time.
At the annual meeting, the company said it remained committed to the daigou infant formula trade into China, despite it being responsible for clouding its short-term earnings outlook.
Daigou, "buying on behalf of", covers the unofficial group of individuals who shop and send products to China for a profit.
Over the last three years, the daigou trade in a2 Milk infant formula has developed along corporate lines, with most operators based in Victoria, which has been the hardest hit of any of the Australian states by Covid-19 lockdowns.
A2 Milk shares last traded at $14.12, having dropped by 7.11 per cent over the last 12 months.