U.S. Sen. Cory Gardner was among 12 Republican senators Tuesday who co-signed a letter sent to U.S. Attorney General Jeff Sessions calling on the Trump Administration to stop its current policy of separating families who enter the United States illegally, a practice that has ignited a nationwide outcry and drawn action from Gov. John Hickenlooper in Colorado.

Separately, Republican Rep. Mike Coffman went on National Public Radio and said the policy must end.

A release from Gardner’s office on Tuesday said his letter asks the administration to halt its current policy of separating children from their parents who enter the country unlawfully and for the practice to be stopped while Congress attempts to “fix the issue through legislation.”

Gardner has supported immigration reform proposals in the past, voting for legislation in February. He wrote Monday on Twitter that the country’s immigration system “is broken & the separation of children at our southern border shows just how critical it is that Congress pass immigration reform immediately.”

“Children should not be penalized for the actions of their parents, & that’s exactly what is happening right now,” Gardner wrote in the tweet.

In response to the federal policy, Hickenlooper on Monday signed an executive order banning the state government from assisting the feds in implementing this policy. The Trump Administration has defended the policy, with both Sessions and Homeland Security Secretary Kirstjen Nielsen backing the practice.

Here’s the letter in its entirety:

“Like millions of Americans, we have read with increasing alarm reports of children being separated from their parents at the southern border. Although enforcing our immigration laws is an essential responsibility of the federal government, it must be done in a way that is consistent with our values and ordinary human decency.

The current family separation crisis has multiple contributing causes, including court decisions that require release rather than detention of children but not parents who enter our country illegally. But the immediate cause of the crisis is your Department’s recent institution of a ‘zero tolerance’ policy under which all adults who enter the United States illegally are referred for prosecution, regardless of whether such individuals are claiming asylum and regardless of whether they are accompanied by minor children.

We support the administration’s efforts to enforce our immigration laws, but we cannot support implementation of a policy that results in the categorical forced separation of minor children from their parents. We therefore ask you to work with the relevant Administration officials to stop the separation of families pursuant to the Department’s zero tolerance policy while Congress works out a solution that enables faster processing of individuals who enter our country illegally. We believe a reasonable path forward can be found that accommodates the need to enforce our laws while holding true to other, equally essential values.”

Other Republican Senators who co-signed the letter include Orin Hatch of Utah, John McCain of Arizona, Pat Roberts of Kansas, Susan Collins of Maine, Lisa Murkowski of Alaska, Bob Corker of Tennessee, Lamar Alexander of Tennessee, John Boozman of Arkansas, Dean Heller of Nevada, James Lankford of Oklahoma, and Bill Cassidy of Louisiana.