Thirty U.S. senators will vote today over whether there really are 5 million Palestinian "refugees" or just around 30,000 -- a hot-button issue that has already become the subject of a vigorous international debate involving Israel and its Arab neighbors.

When the Senate Appropriations Committee takes up the fiscal 2013 State Department and foreign operations appropriations bill today, senators will vote on an amendment crafted by Sen. Mark Kirk (R-IL) that would require the State Department to report on how many of the millions of people currently supported by the United Nations Relief and Works Agency for Palestinian Refugees (UNRWA) are actually people who were physically displaced from their homes in Israel or the occupied territories, and how many are descendants of original refugees.

The amendment is just a reporting requirement and doesn't change the way the United States classifies refugees or how it gives more than $250 million annually to UNRWA, about a quarter of the agency's budget. But a battle is already raging behind the scenes over what it might mean if the State Department started separating original Palestinian refugees from their descendants, and opponents of the Kirk amendment fear the end goal is to cut off U.N. aid to millions of Palestinians.

Here's the actual text of the Kirk amendment that will be introduced today, obtained in advance by The Cable:

United Nations Relief and Works Agency.- Not later than one year after the enactment of this Act, the Secretary of State shall submit a report to the Committees on Appropriations detailing the number of people currently receiving United Nations Relief and Works Agency (UNRWA) services 1) whose place of residence was Palestine between June 1946 and May 1948 and who were personally displaced as a result of the 1948 Arab-Israeli conflict ("such persons"); 2) who are children of such persons; 3) who are grandchildren of such persons; 4) who are descendants of such persons and not otherwise counted by criteria (2) and (3); 5) who are residents of the West Bank or Gaza; 6) who do not reside in the West Bank or Gaza and are citizens of other countries; and 7) whose place of residence was Palestine between June 1946 and May 1948, who were personally displaced as a result of the 1948 Arab-Israeli conflict, who currently do not reside in the West Bank or Gaza and who are not currently citizens of any other state.

Asked for comment by The Cable, Kirk's spokesperson Kate Dickens said that nothing in the Kirk amendment would change U.S. policy toward refugees nor directly threaten any funding for UNRWA.

"The amendment simply demands basic transparency with regard to who receives U.S. taxpayer assistance," she said. "A vote against this amendment is a vote to deny taxpayers basic information about an agency they are funding."

Critics of the amendment say they fear the amendment is just the first step in a longer effort to cut off funding for UNRWA and deny millions of Palestinians the "right of return" to lands their parents or grandparents lost in 1948 or 1967.

A May 21 article by Jonathan Schanzer, vice president at the Foundation for the Defense of Democracies, tied the two issues together directly.

"The aim of this proposed legislation, Kirk's office explains, is not to deprive Palestinians who live in poverty of essential services, but to tackle one of the thorniest issues of the Palestinian-Israeli conflict: the ‘right of return,'" he wrote. "The dominant Palestinian narrative is that all of the refugees of the Israeli-Palestinian wars have a right to go back, and that this right is not negotiable. But here's the rub: By UNRWA's own count, the number of Palestinians who describe themselves as refugees has skyrocketed from 750,000 in 1950 to 5 million today. As a result, the refugee issue has been an immovable obstacle in round after round of negotiations between the Israelis and Palestinians."

It's true that Kirk's original language, submitted as a request to Senate Appropriations State and Foreign Ops Subcommittee Chairman Patrick Leahy (D-VT), called for a change in U.S. policy in how to define Palestinian refugees.

"It shall be the policy of the United States with regard to the United Nations Relief and Works Agency (UNRWA) that a Palestinian refugee is defined as a person whose place of residence was Palestine between June 1946 and May 1948, who was personally displaced as a result of the 1948 or 1967 Arab-Israeli conflicts, who currently does not reside in the West Bank or Gaza and who is not a citizen of any other state," the original language stated, according to a copy of the text obtained by The Cable.

But after Leahy declined to include that language in his section of the overall bill on May 22, Kirk's office worked with other Senate offices and outside groups like AIPAC to craft compromise language that would be less aggressive.

After the final language was crafted, requiring only a report and not changing U.S. policy, Leahy still demurred. The fear was that Israel's neighbors, such as Jordan with an estimated 2 million Palestinian refugees, might object to any effort that could somehow lead to less support for those refugees from the international community.

An intensive background set of discussions took place between Leahy, the State Department, Kirk's office, and the Jordanian Embassy, two congressional aides told The Cable. Initially the Jordanians were inclined to oppose the amendment and agreed with Leahy, but after being given the final text, decided not to weigh in on what is essentially an internal U.S. government reporting requirement.

"The government of Jordan has informed congressional staff they do not oppose the Kirk amendment," one senior GOP Senate aide said. "That is definitely the correct decision for a foreign government, as this is simply a request for info on behalf of the U.S. taxpayer to the U.S. state department."

Ahead of today's vote, AIPAC has been contacting various Senate offices to urge them to support the Kirk amendment, multiple Hill sources said. Democrats slightly outnumber Republicans on the committee, but Democrats have been known to break party ranks on Israel- related issues before.

At the heart of the issue is how to define refugees. UNRWA has been using a definition that includes descendants of refugees while other U.N. bodies, such as the Human Rights Council, does not include descendants in its definition.

The Cable asked State Department spokeswoman Victoria Nuland at Wednesday's press briefing which definition the administration agreed with. She didn't know and the State Department wasn't able to provide an answer after the briefing.

For the people involved in the issue on the ground, the distinction is not as important as the U.N. mission to feed and support these 5 million Palestinians. They see the Kirk amendment as part of a pattern of legislative moves against UNRWA in the U.S. Congress, including a drive to cut off U.S. funding by House Foreign Affairs Chairwoman Ileana Ros-Lehtinen (R-FL).

They also note that the drive to redefine how UNRWA classifies refugees is supported by Israeli President Bibi Netanyahu and a similar drive is led in the Israeli parliament by lawmaker Einat Wilf.

"There are some individuals that believe if they unilaterally in America make changes, that will solve peace processes, and that's really naïve," one U.N. official said. "It has to be done by the parties involved, not the U.S. Congress."

The amendment will likely be submitted by Senate Appropriations State and Foreign Ops subcommittee ranking Republican Lindsey Graham (R-SC), because Kirk is still recovering from a stroke.