President Trump’s discretionary budget plan set to be released Thursday reportedly includes a request for $2.6 billion in funding to begin planning and building a “physical wall” along the border with Mexico along with security funding.

The Wall Street Journal reported that Tump will ask Congress for billions in new spending to be earmarked ofr immigration enforcement. The paper reported that even if Trump's request is granted, the amount of money would not even come close to the amount of money needed to complete the project.

The Department of Homeland Security estimated that a border wall would cost $21 billion. There is also debate on whether or not a physical wall spanning the entire country is needed.

“I support border security, but I think we need a little more definition of what the plan is.” Sen. John Cornyn, R-Texas, told the paper. “I would propose we come up with a plan and then we can come up with when and how to fund it.”

The warning from Senate Minority Leader Chuck Schumer and others came in a letter Monday to Majority Leader Mitch McConnell of Kentucky. The letter also warns against adding other "poison pills" such as provisions to roll back environmental or consumer protections and urges additional money for domestic programs to match the administration's planned Pentagon increases.

"We believe it would be inappropriate to insist on the inclusion of (wall) funding in a must-pass appropriations bill that is needed for the Republican majority in control of the Congress to avert a government shutdown so early in President Trump's administration," said the letter, which was provided to The Associated Press.

Trump's proposal for the wall was a centerpiece of his presidential campaign and he claimed he could persuade Mexico to pay for it.

The Associated Press contributed to this report