GOP frontrunner Donald Trump explains how he plans to force Mexico to pay for his proposed border wall in a two-page memo to The Washington Post.

“In the memo, Trump said he would threaten to change a rule under the USA Patriot Act antiterrorism law to cut off a portion of the funds sent to Mexico through money transfers, commonly known as remittances,” the Post reports. “The threat would be withdrawn if Mexico made ‘a one-time payment of $5-10 billion’ to pay for the border wall, he wrote.”

“It’s an easy decision for Mexico,” Trump states in the memo.

According to the Post, Mexicans living outside their home country sent roughly $25 billion home in 2015. Trump writes in the memo that “the majority of that amount comes from illegal aliens.” However, the Post notes the $25 billion includes cash from all over the world – not solely from the United States.

Economists told the Post that this flow of cash is vital for the Mexican economy.

The memo also suggests increased trade tariffs, visa cancelations and increasing border-crossing card fees could help aid in the plan to make Mexico pay for the wall.

Trump has predicted the border wall would cost roughly $8 billion.