The U.S. Environment Protection Agency (EPA) is facing a lawsuit due to the decline of monarch butterflies in the country.

The National Resources Defense Council (NRDC), an environment advocate group, has filed the lawsuit in a U.S. district court in New York, which alleges that EPA dismissed the dangers related to glyphosate, an ingredient used in herbicides. The lawsuit states that the use of herbicides has drastically reduced the population of monarch butterflies.

NRDC explains that glyphosate terminates milkweed, which is the only food that monarch butterflies consume when migrating. The latest lawsuit claims that the laws in the U.S. require the EPA for ensuring that any pesticides the agency approves does not cause adverse effects on the environment, including wildlife. NRDC's lawsuit alleges that EPA never took into account the adverse effects of glyphosate on monarch butterflies.

In early 2014, NRDC as well as some other environmental advocate groups submitted a petition to the EPA, which asked the agency to review the scientific evidences that reflected at the use of glyphosates and its effects on monarchs; however, EPA failed to respond to the petition.

Monarch butterflies cannot bear extreme cold winters and millions of monarchs migrate from the U.S. and Canada to Mexico in search of warmer climate.

NRDC suggests that the latest annual migration of monarch butterflies to Mexico had about 56.5 million butterflies, which is supposed to be the second lowest approximation on record. However, the World Wildlife Fund (WWF) estimated that around 27.48 acres of the Mexican refuge was covered by the monarchs in 2015, which is an increase when compared to 2104.

"It is crucial that we restore and protect the habitat of this iconic species in all three countries, but above all that we limit the use of herbicide and land conversion in the United States and maintain efforts to avoid deforestation in Mexico," says Omar Vidal, Director General of WWF in Mexico.

The EPA is defending the lawsuit and suggests that it is taking measures to stop any further decline in monarch butterflies population.

"With regard to pesticide exposure, EPA is looking holistically at all herbicides, not only glyphosate, to determine the effects on monarchs and resources critical to butterfly populations," per an EPA statement.

Recently, the U.S. Fish and Wildlife Service has also announced that it will launch a campaign worth $3.2 million in an effort to save the natural habitat of the monarchs.