Rigoberto Valderrama Padilla has been living in San Diego for 30 years. Originally from Acapulco, Mexico, he now works for a construction company and regularly sends remittances for food and other necessities to his family back home. “This income is crucial for them. I want to help however I can,” Valderrama says. He is not the only one.

Every month, U.S. residents like Valderrama send $2 billion across the border to their families in Mexico. More than 6 million Mexicans, or about 7 percent of the adult population, benefit from such remittances, which collectively account for nearly 3 percent of the country’s economy.

These figures include all remittances, of which American remittances account for more than 90 percent.

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But that steady stream of cross-border cash could soon be in jeopardy. As part of his plan to make Mexico pay for a border wall, Donald Trump has said he will demand the country “make a one-time payment of $5-10 billion” if it wants to protect the flow of remittances. Mexican President Enrique Peña Nieto has said repeatedly that the country won’t pay for the wall, meaning that if Trump follows through on his threats, millions of Mexican families could soon lose out on a vital source of income.