The EPA began investigating Dacthal or DCPA herbicides last week after they were pulled off shelves in the United States.
It is now urging people to avoid the herbicide used to control annual grasses and broadleaf weeds in vegetable growing globally.
Dr Shaun Presow, a hazardous substances reassessments manager, said the EPA has issued the alert because it has serious concerns about the potential risks to people's health.
"We urge anyone currently using a product containing chlorthal-dimethyl to stop and to consider alternatives.
"If people can't avoid using these products, the EPA advises they take all precautions to avoid exposure for people who are pregnant or could be pregnant."
This includes restricting access to sprayed areas and making sure nobody else is around during spraying, Presow said.
The US Environmental Protection Agency found a risk of thyroid hormone changes in the unborn children of pregnant bystanders, women who apply chlorthal-dimethyl, or those who enter treated fields after the substance has been applied.
These changes can cause low birth weight and irreversible and life-long impacts, such as impaired brain development and motor skills.
EPA had set up a working group to look at how this herbicide is being used here, and to take rapid action to ensure it continued protecting people's health and safety, he said.
"While this is happening, we have put out a red alert to ensure the public is aware of the potential risks."
The EPA is consulting with those likely to be affected by any proposed additional rules around the use of DCPA herbicides.
