Law firm Slater and Gordon is investigating a possible class action claim against a2 Milk in relation to its disclosure over a nine-month period when it announced four earnings downgrades.

During this time the shares slumped around 60 per cent, plunging its market cap from $8.2 billion to $4.2b.

Slater & Gordon alleges a2 Milk may have engaged in misleading or deceptive conduct in breach of the Corporations Act; and possibly breached continuous disclosure rules pointing to four downgrades, according to the Australian Financial Review.

"Our investigation is considering whether or not all of the information that's been dripped out by the company over the last nine months was actually not in the company in August when they gave that initial full-year guidance."

A2 Milk responded in a statement to the NZX saying it was not aware of any legal proceedings, although it was aware of the AFR report.

"The company is not aware of any legal proceeding having been filed at this time," it said.

"The company believes that it has complied with all applicable disclosure obligations and denies any claim to the contrary. The company will respond further if and when any legal proceedings are commenced."

On May 10, a2 slashed its revenue and earnings forecasts for the 2021 financial year in a fourth consecutive downgrade and said it was reviewing its key China business amid fresh provisioning of more than $100m of inventory.

The dual listed company is now targeting revenue for 2021 of $1.20 billion to $1.25b, down from an earlier forecast of $1.4b, and group EBITDA margins of 11-12 per cent, compared to 30-31 per cent.

The company said the trading dynamics in the China infant nutrition market have been and continue to be challenging for a2 Milk and many international competitors.

"While a2 Milk's third quarter trading was broadly in line with plan, it is clear that the actions taken to address challenges in the daigou/reseller and CBEC channels will not result in sufficient improvement in pricing, sales and inventory levels to meet its previous guidance," it said.