Cardinal Daniel DiNardo, the Archbishop of Galveston-Houston in Texas, said the new president's actions "deeply concern me".
It's after President Trump signed an executive order earlier this week to move forward with building the 2000-mile wall, which will cost billions of dollars and require approval from Congress first.
The President said at the time: "I've just signed two executive orders, that will save thousands of lives, millions of jobs, and billions and billions of dollars.
"A nation without borders is not a nation. Beginning today, the United States of America gets back control of its borders."
Trump has repeatedly claimed Mexico will pay for the wall, however Mexican President Enrique Pena Nieto has consistently denied the country would pay a penny.
Cardinal DiNardo said in a statement: "As Archbishop of a Texas diocese, I believe that the order to construct a wall along our border with Mexico will only make migrants more susceptible to traffickers and smugglers - putting their lives in needless danger.
"It also destabilizes the many vibrant interconnected communities that live in peace along our border.
"The Archdiocese of Galveston-Houston is committed to an immigration policy that protects human rights, dignity and the homeland at the same time. Over the years, we have seen first-hand the suffering caused by a broken immigration system."
