Micheál Martin has said that he cannot understand why the Taoiseach is refusing to take part in a leaders' debate on the EU Fiscal Treaty.
Enda Kenny will address the nation unchallenged on Sunday night, calling for a Yes vote on May 31. This has prompted criticism from those opposed to the Treaty.
RTÉ said that it offered the address to provide balance to coverage of the Sinn Féin Ard Fheis.
Mr Martin said that leaders of political parties should be prepared to take part in a debate.
"Well I don't understand the Taoiseach's reasoning behind that, that's a matter for the Taoiseach," he said.
"I personally have a view in politics that for leading parties we should be prepared to take part in debates."