Texas, Arkansas, Indiana and Louisiana on Monday joined two other U.S. states in saying they will no longer accept Syrian refugees, contending it is too dangerous to let in people from that war-torn country following Friday’s deadly Paris attack.

Republican Governors Greg Abbott of Texas, Asa Hutchinson of Arkansas, Mike Pence of Indiana and Bobby Jindal of Louisiana, followed the lead of Alabama and Michigan in saying their states would no longer help support the Obama administration’s goal of accepting 10,000 Syrian refugees in the coming years.

“Texas cannot participate in any program that will result in Syrian refugees – any one of whom could be connected to terrorism – being resettled in Texas,” Abbott said in an open letter to U.S. President Barack Obama on Monday. “Neither you nor any federal official can guarantee that Syrian refugees will not be part of any terroristic activity.”

But it was unclear what authority governors had to stop admitting refugees into their states, legal experts said.

“The federal government has the power over immigration. If they admit Syrian refugees, they’re here,” said Deborah Anker, a professor of law at Harvard Law School who specializes in immigration issues. “People aren’t going to the (state) border. The federal government is going to bring them in.”

The United States admitted 1,682 Syrian refugees in the federal fiscal year that ended Sept. 30, a sharp jump from the 105 admitted a year earlier. Texas, California and Michigan accepted the largest number of people fleeing the war.