Republican senators demanded that the Obama administration produce a plan to deal with U.S. passport holders who have joined the Islamic State in Iraq and Syria (ISIS).

Sens. John ThuneJohn Randolph ThuneTrump endorses Murkowski challenger Yellen: Disclosure of tax data to ProPublica a 'very serious situation' Sanders won't vote for bipartisan infrastructure deal MORE (R-S.D.) and Bob CorkerRobert (Bob) Phillips CorkerCheney set to be face of anti-Trump GOP How leaving Afghanistan cancels our post-9/11 use of force The unflappable Liz Cheney: Why Trump Republicans have struggled to crush her  MORE (R-Tenn.) led a group of 14 Republicans in sending Secretary of State John Kerry and Homeland Security Secretary Jeh Johnson a letter on Thursday. They wrote that the administration hasn’t released a comprehensive plan for tracking and preventing ISIS members from traveling to the U.S. to potentially carry out terrorist acts.

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“We write today to encourage you to take immediate action to prevent U.S. and western country passport holders fighting alongside the Islamic State of Iraq and Syria (ISIS), Jabat al-Nusra or other terrorist organizations from traveling to the U.S. to commit acts of terrorism against the homeland,” the letter stated.

The senators cited a statement from Defense Secretary Chuck Hagel saying more than 100 U.S. citizens with passports are fighting with ISIS in the Middle East.

In the letter, senators write that Kerry has the authority to revoke the U.S. passport of any citizen who poses a threat to national security and that the passport-holders' names should be added to the FBI’s “No-Fly List.”

They also asked the administration to explain how they are working with visa waiver countries, such as those in Europe, to ensure no individual with ties to terrorism could enter the United States by means of their country.

Their letter came after President Obama outlined his plan to deal with the growing ISIS threat in the Middle East after the terrorist group have gained control of large swaths of land in the region and beheaded two U.S. journalists.