(Bloomberg) -- A judge stopped short of barring President Donald Trump from diverting billions of dollars in the federal budget to pay for his promised border wall, but ruled that plans to build sections of the barrier can’t go forward without his review.

The injunction specifically prohibits the administration from starting work at two sites where contracts have been awarded, in Arizona and Texas. Parties have been asked to appear again before U.S. District Judge Haywood Gilliam in Oakland, California, on June 5 to argue the merits for a more comprehensive injunction and a possible trial, according to the judge’s order.

Central to the Justice Department’s argument was the idea that since Congress had not explicitly told Trump not to divert the funds from the 2019 budget, he was entitled to use his presidential powers to reallocate the money he needs to build sections of the wall. Judge Gilliam rejected the argument.

This “does not square with fundamental separation of powers principles dating back to the earliest days of our Republic,” Gilliam said in his 56-page opinion issued late Friday. “Congress’s ‘absolute’ control over federal expenditures -- even when that control may frustrate the desires of the Executive Branch regarding initiatives it views as important -- is not a bug in our constitutional system.”

The president campaigned on a promise to build a wall, paid for by Mexico, on his path to the White House in 2016. As he runs for re-election in 2020, a protracted legal battle over how to pay for the project may ultimately end up before the U.S. Supreme Court.

Migrant Crossings

The number of migrants attempting to cross the southwestern border has surged as violence, economic turmoil and climate change trigger crises in Mexico and its Central American neighbors, Guatemala, Honduras and El Salvador. More than 109,000 people tried to cross in April, with 90 percent skirting official ports of entry, according to government data.

Trump has been unable to reach a consensus with a divided Congress on immigration reform, and his latest plan for a comprehensive overhaul is getting a cold reception even within the ranks of Republican lawmakers.

To move forward with the wall project, the Defense Department transferred $1 billion to the Army Corps of Engineers on March 25. The administration awarded its first contract for construction in Yuma, Arizona, on April 9, but the award was challenged by the Government Accountability Office within 10 days and scrapped on May 4.

The funds earmarked for reallocation are primarily coming from drug interdiction and enforcement activities. Court records show that the role of the military in construction of the wall is still under discussion.

Gilliam is likely to evaluate the legality of the funding for each project as it’s proposed rather than issue the sweeping injunction sought by opponents of the wall including the Sierra Club and a coalition of about 20 state attorneys general, among others.

The American Civil Liberties Union and a group of 16 state attorneys general led the attack against the president’s emergency declaration. The ACLU called today’s order a win for checks and balances.

“The court blocked all the wall projects currently slated for immediate construction,” said Dror Ladin, staff attorney with the ACLU’s National Security Project. “If the administration begins illegally diverting additional military funds, we’ll be back in court to block that as well.”

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