Sen. Rand Paul (R-Ky.) sent a letter Monday criticizing Republican leaders, in particular House Speaker John Boehner (R-Ohio), for not pushing a balanced-budget amendment in a deal to raise the debt ceiling.

In the letter sent through nonprofit group Campaign for Liberty — his father, Rep. Ron Paul's (R-Texas) — Paul attacks the "Washington establishment" for pushing a deal to raise the debt limit "without really changing the way Washington works."

"You've probably seen reports of these rumored deals and know that Speaker Boehner and others don't seem to have a plan to force the issue of balancing the budget," Paul wrote in the letter.

"Republicans should reject any debt ceiling deal that does not include a Balanced Budget Amendment and spending cuts," Paul wrote. "A Balanced Budget Amendment doesn't even require the signature of the President. It simply needs Congress to stand up and act."

The letter provides more evidence for what some have speculated could be a widening rift within the Republican party when it comes to the debt-ceiling negotiations.

Some within the party would like to insist on opposing any increase in tax revenues or place conditions including spending caps or a balanced-budget amendment, while others, including Boehner, are perceived as more willing to reach a compromise with the White House.

In the same email, Campaign for Liberty urged supporters to contribute money for the group's plan to run "radio, TV and newspaper ads" a few days before the eventual debt-ceiling vote.