Sen. Ted Cruz, R-Texas, and Sen. Rand Paul, R-Ky., will work to block a $1 billion Ukraine aid package unless Senate Majority Harry Reid, D-Nev., strips out a controversial measure funding the International Monetary Fund.

The lawmakers told Reid they "intend to object to any floor consideration of Ukraine aid legislation" until the IMF language is pulled from the bill. Rand and Cruz united on the issue just days after tensions ran high between them because of their disagreements on foreign policy.

"As we understand it, this reform would double the funds the IMF can loan, involving a doubling of the United States' contribution from its current level of $63 billion, while simultaneously reducing U.S. influence over how these funds are directed -- and increasing that of Russia," they wrote to Reid in a March 13 letter released late Friday. "Regardless of the magnitude of this change, this idea is antithetical to the driving purpose of the underlying legislation."

Sen. Mike Lee, R-Utah, also signed the letter to Reid, along with Sen. Mike Enzi, R-Wyo., and Sen. Pat Roberts, R-Kan.

"[The letter] is intended as both personal opposition to any votes advancing the bill as long as it has the IMF piece in it, and to any agreements on anything less than full process on the bill unless such agreement includes a vote on stripping the IMF provisions out," Cruz spokeswoman Catherine Frazier told the Washington Examiner.

Conservatives oppose the IMF provisions because they increase the amount of taxpayer money that can be used to bail out foreign countries and diminish U.S. control of the organization.

"[T]he U.S. would lose its current right to appoint its own representative to the board -- the epicenter of power at the IMF," the Heritage Foundation's James Roberts explained Monday.

Sen. Bob Corker, R-Tenn., the top Republican on the Foreign Relations Committee, supports the bill with the IMF provisions.

“We're all looking to the IMF to be that organization that really moves Ukraine along and I just don't know how we cannot honor the commitments to the IMF that we have,” Corker explained to The Daily Beast.

Cruz and Paul's alliance on this issue comes after tensions ran high between the two because Cruz made a comment that Paul viewed as Cruz trying to claim the mantle of Ronald Reagan at his expense.

"I think U.S. leadership is critical in the world," Cruz said on ABC. "And I agree with him that we should be very reluctant to deploy military force aboard. But I think there is a vital role, just as Ronald Reagan did."

"I don't claim to be the next Ronald Reagan nor do I attempt to disparage fellow Republicans as not being sufficiently Reaganesque," Paul shot back in a Breitbart op-ed clearly aimed at Cruz. "But I will remind anyone who thinks we will win elections by trashing previous Republican nominees or holding oneself out as some paragon in the mold of Reagan, that splintering the party is not the route to victory."