President Donald Trump is going to ask Congress for $1.5 billion to begin work on the wall he promised to build at the U.S.-Mexico border, reports The Hill. 

According to White House budget director Mick Mulvaney, the money is only a small part of a $30 billion supplemental spending request that’s being sent to lawmakers today (Thursday, March 16). It’s expected that the request will trigger a giant showdown between the parties, as the “wall” is a super controversial discussion.

The wall is Trump’s effort to crack down on illegal immigration, a topic that roused many voters during this campaign. “The Wall” was a promise he made to voters, and at the beginning of the campaign he even “promised that Mexico would pay for it.”

The Hill reports that Senate democrats have warned Republicans they could risk a government shutdown ahead of a funding deadline next month if they insert “poison pill,” like money for the wall, into spending bills.

However, Mulvaney said to reporters that the money is to be used to start developing technologies and locations for the wall.

Trump is also going to ask for $2.6 billion in funding for the wall in his fiscal year 2018 budget request. the document is Trump’s “toppling” budget for next year and doesn’t include protections over a decade. The full funding request for the wall could come as early as May, added The Hill.

“We believe it would be inappropriate to insist on the inclusion of such 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,” Democratic leaders wrote in a letter this week.

Lawmakers have until April 28 to pass a measure to keep the government funded and avoid a shutdown.