Sen. Chuck Grassley is pressing the administration for information on Cuban nationals in the U.S., suggesting the administration failed to get Havana’s cooperation on repatriation during recent talks.

The Iowa Republican in a letter to Secretary of State John Kerry and Homeland Security Secretary Jeh Johnson said the recent negotiations between the United States and Cuba offered a “singular opportunity” to require that Cuba take back some of its nationals who have been ordered to leave the U.S. as a requirement to restoring diplomatic ties.

{mosads}”I write to you to express my concern about the Cuban government’s continuing failure to cooperate with the United States in the repatriation of its nationals with final orders of removal and my disappointment that the Administration has failed to use the negotiations leading up to the re-establishment of diplomatic relations … to address the issue of repatriation,” Grassley, the chairman of the Senate Judiciary Committee, wrote in a letter sent late last week that was released on Monday.

Grassley added that he wants the two administration officials to explain if, and to what extent, U.S. diplomats tried to get Cuba to commit to taking back nationals who have been ordered to leave the U.S.

He’s also pushing Kerry and Johnson to say if repatriation would be included in further talks with Cuba, and why they think it will be successful, because “the U.S. has given away the enormous political/diplomatic leverage it had against Cuba.”

He also wants to know if the administration has ruled out using visa sanctions, which would make it harder for Cubans to travel to the United States, to try to get Cuba to cooperate.

The United States and Cuba reopened their embassies earlier this year as part of a months-long effort to restore and improve diplomatic relations between the two countries.

Grassley also wants the administration to hand over a range of details on Cuban nationals in the country who have been ordered to leave, including how many there are in total, how many have criminal records, and a breakdown of how long it’s been since they ordered to leave.

The Iowa Republican, in the letter, said that he believes there are currently 34,000 Cuban nationals in the United States who have been ordered to leave, and that “many are apparently convicted criminals.”

He also points to 2011 testimony from a former Immigration and Customs Enforcement official who laid out steps the government could take to try to force countries to take back their nationals. Grassley wants the administration to hand over a timeline of what, if any, steps have been taken.

He added that if steps haven’t been taken he wants an explanation, because “Cuban recalcitrance regarding repatriation has been a problem for decades, and tens of thousands of Cuban criminals with final orders of removal freely walk the streets of the United States.”

The letter comes after the Iowa Republican slammed the administration last week for what he suggested was a slow response rate to his inquires. He’s blocking roughly 20 foreign officer nominations over the incident.