The leaders of the Senate Homeland Security and Governmental Affairs Committee are seeking details on federal efforts to prevent shipments of powerful synthetic opioids from entering the United States.

Chairman Ron Johnson Ronald (Ron) Harold JohnsonThis week: Supreme Court fight over Ginsburg's seat upends Congress's agenda GOP set to release controversial Biden report Democrats fear Russia interference could spoil bid to retake Senate MORE (R-Wis.) and the panel’s top Democrat, Sen. Claire McCaskill Claire Conner McCaskillMomentum growing among Republicans for Supreme Court vote before Election Day Democratic-linked group runs ads in Kansas GOP Senate primary Trump mocked for low attendance at rally MORE (Mo.), sent letters Monday to the State Department, the Department of Homeland Security and the U.S. Postal Service requesting the information.

“The opioid crisis in this country has reached epidemic proportions, and it is a multifaceted problem that demands a whole-of-government approach to resolve,” the senators wrote.

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“While the causes of drug addiction are complex, the U.S. has seen an increase in the presence of synthetic opioids, like fentanyl and fentanyl analogs, which can easily be purchased from the ‘dark web.’”

McCaskill and Johnson want to know about the agencies’ efforts to stop fentanyl from being shipped to the U.S. from China and other countries.

The senators are requesting details such as how the agencies and foreign postal operators are working together to share data, the extent of the problem and the degree to which current guidelines are followed, among other issues.

The senators are requesting that the information be provided by Dec. 15.

Synthetic opioids are a major contributor to the spike in U.S. opioid overdose deaths.

From 2014 to 2015, the death rate from synthetic opioids jumped 72 percent, according to the Centers for Disease Control and Prevention.