WASHINGTON (Reuters) - Two U.S. Senate Democrats have written to President Donald Trump’s nominee to head up the U.S. consumer watchdog agency, seeking documents to determine whether she had a role in the administration’s policy of separating immigrant children from their families.

Immigrant children, many of whom have been separated from their parents under a new "zero tolerance" policy by the Trump administration, are shown walking in single file between tents in their compound next to the Mexican border in Tornillo, Texas, U.S. June 18, 2018. Picture taken June 18, 2018. REUTERS/Mike Blake

Trump on Monday formally nominated Kathy Kraninger, a senior official at the Office of Management and Budget (OMB), to head the Consumer Financial Protection Bureau (CFPB), drawing criticism from Democrats and consumer advocates, and dividing Republicans.

The letter from Senators Elizabeth Warren and Sherrod Brown dated June 18 could drag Kraninger into the controversy over the administration’s policy of detaining children separated from their parents at the U.S.-Mexico border. The policy has caused a national uproar and divided Republicans, potentially threatening Kraninger’s nomination.

Brown and Warren said they want information on what role Kraninger played in the administration’s “cruel policy” to separate children from their families. The senators said she has been involved in overseeing policies implemented by the Department of Homeland Security (DHS) and the Justice Department.

OMB representatives did not immediately respond to a request for comment.

In April, U.S. Attorney General Jeff Sessions announced a “zero tolerance” policy that all immigrants apprehended while crossing the U.S.-Mexico border illegally should be criminally prosecuted under the country’s criminal entry statute. The policy has led to family separations because when border agents refer apprehended migrants to court for criminal prosecution, parents are held in federal jail to await trial while the children either remain in border patrol custody or are moved into facilities managed by the Office of Refugee Resettlement, a Department of Health and Human Services agency.

Democrats have accused the administration of “barbaric” treatment of children, while Republicans are moving tentatively toward legislation that would curb, if not entirely halt, the practice.

Kraninger has helped prepare the president’s annual budget request for the DHS and Justice Department, including “ongoing policy and management guidance” and overseeing the “implementation of policy options,” Warren and Brown said.

The senators were seeking to determine her role, if any, in implementing the “zero tolerance” policy, they said.

(This story corrects paragraph 1 to show that separated families did not necessarily cross the border illegally; Rephrases paragraph 6 on ‘zero tolerance’ policy, family separations.)