A Republican governor has balked at sending National Guard troops to the US border in the wake of the Trump administration’s “inhumane treatment” of children.

Massachusetts Gov. Charlie Baker said Monday that “we told the National Guard to hold steady and to not go down to the border — period,” according to NBC 10 Boston. “We won’t be supporting that initiative unless they change the policy.”

He pulled back troops because “the federal government’s current actions are resulting in the inhumane treatment of children,” said Lizzy Guyton, the governor’s communications director, in a statement.

Baker had announced earlier this month that he would comply with Trump’s request to send National Guard personnel down to the border. None had been deployed, and Massachusetts’s contribution was modest: just a helicopter and two analysts, according to the Boston Globe.

“I’m hopeful that with the voices that are coming out at this point and making that case to them, that they will consider alternatives to deal with border security,” Baker said Monday, according to NBC 10 Boston. “Border security is important — no one disputes that — but separating kids from their families is not.”

The reversal came as the Trump administration pursues a “zero-tolerance” policy against people illegally crossing the border, even if they’re seeking asylum. The policy has resulted in the separation of families; between April 19 and May 31, approximately 2,000 kids were separated from their parents.

The Trump administration signed a proclamation in April to have states send National Guard troops to the US-Mexico border. Texas and Arizona, both southwestern border states, had sent troops. As Vox’s Dara Lind explained at the time, how the National Guard would assist border agents wasn’t entirely clear; National Guard troops aren’t authorized to arrest or participate in arrests of migrants and aren’t armed. Politico reported last week that National Guard troops were mostly in support roles, doing somewhat menial tasks like tending to horses and changing flat tires.

Previous administrations, including Obama and Bush, deployed National Guard troops to assist at the border, so Trump’s request wasn’t remarkable for a US president. But his policy pursuing allowing for family separation is — and Baker, though from a blue state, is one of the first prominent (and not retiring) Republicans to take concrete steps to oppose the policy.

Other prominent Republicans have also challenged the administration’s support for family separation. Former first lady Laura Bush wrote an op-ed in the Washington Post in which she suggested the images were “eerily reminiscent” of Japanese-American internment camps during World War II. Her brother-in-law and former presidential candidate Jeb Bush also condemned the practice and blasted Trump for using children as a “negotiating tool.”

Children shouldn’t be used as a negotiating tool. @realDonaldTrump should end this heartless policy and Congress should get an immigration deal done that provides for asylum reform, border security and a path to citizenship for Dreamers. https://t.co/OOjv0vNeVg — Jeb Bush (@JebBush) June 18, 2018

Sens. Jeff Flake (R-AZ) and Susan Collins (R-ME) sent a letter to the Department of Homeland Security about the practice of separating families, and Collins described the policy as “contrary to our values in this country” on Face the Nation on Sunday. But so far, neither has supported legislation that would prevent family separations within 100 miles of the US border, except for instances of abuse or neglect. The bill has support from all 49 Democrats.