Early in the summer, Americans in every state began receiving unsolicited packages filled with seeds. The mystery seeds were originated from China, according to the United States Department of Agriculture.

The USDA quickly urged Americans to not plant the seeds.

U.S. Rep. James Comer Thursday announced that he has sent letters to executives of the Alibaba Group and eBay Inc., expressing his concerns that the platforms have allowed the sale and importation of foreign plants.

“When mystery seeds from China began landing in Americans’ mailboxes, we knew we had a problem,” Comer said in a news release. “State and federal agricultural officials promptly warned the public that these products when planted, pose enormous risks to U.S. agriculture.”

He said that, if planted, invasive plant species could “wreak havoc” or introduce unknown diseases to local crops, livestock or ecosystems.

“In order to protect Americans, it is crucial for companies and their platforms to abide by U.S. Customs laws, which rightfully prohibit sellers abroad from importing seeds,” Comer said.

He added that after the seeds were delivered, Amazon stopped allowing the companies to sell or distribute them.

“Now, it is time for eBay and the Alibaba Group to commit to the same,” he said.