The three lawmakers, sometimes called the "Three Amigos," usually see eye-to-eye on national security issues. But McCain is the leading opponent of Lieberman's cybersecurity bill, which Lieberman has said is his top legislative priority before he retires at the end of the year.
Lieberman's bill, which is co-sponsored by Sen. Susan CollinsSusan CollinsCollins: I'm not working with Freedom Caucus chairman on healthcare Mexico: Recent deportations 'a violation' of US immigration rules White House denies misleading public in aircraft carrier mix-up MORE (R-Maine) and has the support of the White House, would give the Homeland Security Department the authority to require that critical infrastructure such as electrical grids and gas pipelines meet minimum cybersecurity standards.
Supports of the bill say the mandates are necessary to ensure that vital systems are safe from attacks.
But McCain and other Republicans argue the mandates would impose unnecessary burdens on businesses.
A draft of the Kyl-Whitehouse compromise proposal would put the Homeland Security Department in charge of developing a program to pressure, but not force, critical infrastructure companies to better protect their computer systems.
Kyl told The Hill on Tuesday that he's trying to find middle ground, saying cybersecurity is a "very, very important issue that needs to resolved." He declined to discuss specifics of his proposal or which senators are involved.
McCain said he has not participated in the discussions.
He also criticized the compromise proposal, saying it "gives too much authority to Homeland Security."
"I'm not ready to let them write regulations," McCain told The Hill.