The first of 400,000 trees are being planted to form a “green wall” in protest of the fence the U.S. is building along the border with Mexico.

The treeline will eventually stretch for 318 miles (512 kilometers) along the border between the Mexican state of Coahuila and Texas.

Coahuila Gov. Humberto Moreira Valdes says “our wall is of life, and it competes with shame and hate.”

The U.S. government says its fence is critical to security. Critics say it fuels animosity between the two countries and raises environmental and private property concerns.

The mayor of a Texas border town attended Friday’s tree planting in Piedras Negras. Eagle Pass Mayor Chad Foster opposes the ongoing construction of 670 miles (1,080 kilometers) of border fence.