Taoiseach Leo Varadkar has directly asked whether Mary Lou McDonald takes direction from "senior republicans" in her role as Sinn Fein leader.
The comments came in Dail exchanges, with Fianna Fail leader Micheal Martin combining with the Taoiseach to criticise Sinn Fein for failing to provide a nationalist voice in the Brexit crisis.
The Taoiseach said he followed proceedings of the Northern Ireland public inquiry into the so-called "cash for ash" scheme which caused the collapse of Stormont in January 2017.
He was surprised to learn that Sinn Fein had a greater role than was earlier realised.
He pointed to emails, unearthed in the inquiry, from then Sinn Fein finance minister in Belfast, Mairtin O Muilleoir. Mr O Muilleoir had at one point emailed "a senior republican," Ted Howell, who did not hold any elected office, seeking clearance to sign-off for a business plan related to the heating scheme by the following Wednesday.
"That is documentary evidence that Sinn Fein ministers seek approval and consent from 'senior republicans' when it comes to major decisions in government," Mr Varadkar told the Dail.
"I'm just curious to know if Deputy McDonald would want to comment on that, or expand on that, and maybe inform us of the extent she and her front bench require approval from senior republicans for decisions," the Taoiseach added.
The Sinn Fein leader said the Taoiseach should await publication of the full report on the controversial Northern Ireland heat scheme. She said it would record "the central role of the DUP in the affair".
Ms McDonald accused Fine Gael and Fianna Fail of "playing politics" with Northern Ireland's current problems and said the Irish government had an obligation under the Good Friday Agreement to be impartial.
She also argued that Sinn Fein continues to represent the people in Northern Ireland, unlike the other two parties.
Ms McDonald also said she wants to revive power-sharing.