As President Trump’s pick to lead the agency that approves immigration petitions heads towards likely confirmation, more than 300 advocacy organizations are urging the Senate to oppose it, citing ProPublica’s examination of the nominee’s record.

Lee Francis Cissna, a veteran policymaker, was nominated in February to lead the U.S. Citizenship and Immigration Services, the sprawling agency that handles applications for green cards, citizenship, visas, asylum and the controversial deportation protections known as DACA, which benefit 800,000 undocumented immigrants who were brought to the U.S. illegally as children.

In a letter sent Monday to all Senate members, the groups noted that Cissna had volunteered for the Trump campaign and later provided “technical assistance” for Trump’s executive orders on immigration. The letter also referenced a story by ProPublica that showed Cissna helped draft dozens of letters under the letterhead of Sen. Charles Grassley, R-Iowa, between 2015 and 2016. Cissna had worked for Grassley’s office while on loan from his longtime employer, the Department of Homeland Security.

“Mr. Cissna … contributed to a slew of letters criticizing USCIS for implementing various humanitarian programs and initiatives,” the letter read, citing ProPublica. “These include initiatives that reunited families and protected children facing violence, provided young people with Deferred Action for Childhood Arrivals the opportunity to obtain travel documents, and assisted victims of crime, including those affected by domestic and sexual violence.”

In the letter, the organizations urged senators to oppose Cissna’s confirmation or “at the very least,” delay it until after Congress can come up with a permanent legislative solution for DACA. The program was created by President Obama in 2012 through executive action, but its future has recently been the subject of ambiguous statements by the Trump administration.

The letter was signed by some of the biggest immigration advocacy organizations in the country, including the National Immigration Law Center and UnidosUS (until recently known as the National Council of La Raza). A separate letter signed by 45 Latino advocacy organizations, including the Mexican American Latino Defense and Educational Fund was sent on Thursday and also cited ProPublica’s reporting.

In a statement emailed to ProPublica on Monday, Grassley defended Cissna’s nomination.

“Francis Cissna’s remarks at his nomination hearing and responses to written questions from senators demonstrate his deep expertise on immigration policy, which I witnessed first-hand when he was detailed to my office,” Grassley wrote.

Cissna’s nomination sailed through the Senate Judiciary Committee, which is chaired by Grassley, in May with a bipartisan 17-2 vote, but has yet to be voted on by the full Senate. He currently serves as immigration policy director at DHS, where he started working in 2006.

David Lapan, a DHS spokesman, said in an email Monday that Cissna “is well-respected and highly qualified” and noted the support he received at the committee level. “Secretary [John] Kelly looks forward to a confirmation vote by the Senate as soon as possible,” he said.

Early last week, the White House said “unprecedented obstruction” by Senate Democrats had stalled Cissna’s nomination. But on Friday The Washington Times reported that a Republican, Sen. Thom Tillis of North Carolina, had personally intervened to block Cissna’s nomination from reaching the floor until DHS increased the number of temporary visas for unskilled workers this year. On Monday, DHS announced it was adding 15,000 of these visas, known as H-2B. Despite the increase, Daniel Keylin, a spokesman for Tillis, said in an email Monday that the senator was still reviewing the situation and had not decided whether to continue to block Cissna’s nomination.

In written responses during his vetting process, Cissna said he began volunteering about once a week for Trump’s campaign two months before Election Day.

“I offered my expertise in immigration-related policy and operations on a wide variety of projects,” Cissna wrote, “principally relating to employment-based visa policy.”

Cissna has said he personally supports the Trump administration’s efforts to crack down on the perceived abuses of employment visas, notably H-1Bs, which are meant for college-educated foreigners.

In his public comments he has been cautious on DACA, perhaps the most contentious of all immigration programs. At his confirmation hearing in May, he noted that both Kelly and Trump had said that DACA would remain in place, but he did not say he personally supported the program.

“And if confirmed,” Cissna said at the hearing, “I would see my role to be the — to administer that program — as it stands with its current parameters.”

Last Wednesday, however, Kelly met with members of the Congressional Hispanic Caucus and told them he’d been advised that the future of DACA was actually in the hands of the Department of Justice, which would have to decide whether to defend the program in court. He added that several lawyers had advised him that DACA would most likely not survive a legal challenge.

“Kelly was basically telling us DACA is facing a death sentence,” Rep. Luis Gutierrez, an Illinois Democrat, said in a statement about the meeting. Ten Republican state attorneys general have said they will challenge the legality of DACA if the administration does not stop the program by September.

But a day after Kelly’s remarks, Trump appeared to pull rank.

“It’s a decision that I make,” Trump said on the future of DACA while aboard Air Force One, “and it’s a decision that’s very, very hard to make.”