President Obama on Monday asked Congress to set aside $1.9 billion to respond to the Zika virus abroad and to prepare for it in the United States, saying the funds are necessary to halt the spread of the disease and “protect the health and safety of Americans.”

The White House had detailed the outlines of the request earlier this month, arguing that new resources are needed to help ramp up surveillance efforts, control the mosquitoes spreading Zika, accelerate research into new vaccines and diagnostic tests, and help countries already battling the virus.

“This request supports the necessary steps to fortify our domestic health system, detect and respond to any potential Zika outbreaks at home, and to limit the spread in other countries,” Obama wrote in a letter to House Speaker Paul D. Ryan (R-Wis.).

The White House also is seeking flexibility to use some of its unspent funding for the Ebola crisis to respond to Zika or other infectious diseases.

Republicans on Capitol Hill have suggested that the administration first tap unused funds set aside in late 2014 to fight the Ebola epidemic in West Africa before asking for additional money to fight Zika.

In a letter late last week to White House budget director Shaun Donovan, House Appropriations Committee Chairman Harold Rogers (R-Ky.) detailed an array of Ebola funds that remain unused. That includes more than $1.4 billion for the Department of Health and Human Services, as well as funds for the U.S. Agency for International Development, the Centers for Disease Control and Prevention and the National Institutes of Health.

“Before the submission of an emergency supplemental request, it seems incumbent upon the Administration as well as Congress to pursue the use of unobligated funds, including unobligated Ebola funds, which are substantial, to meet the needs of responding to the Zika outbreak,” Rogers wrote.

The bulk of the money the administration is requesting for Zika, about $828 million, would go to the CDC, which has dedicated hundreds of staffers to responding to the outbreak.