The deputy leader of Ennahda has been prevented from entering the US, signaling a possible change in Washington's policy towards the Tunisian Islamist movement.
Politicians and analysts have expressed surprise at the ban on Abdel-Fatah Morro, who is widely known as a moderate figure.
The news dominated the front pages of all Tunisian newspapers.
Morro went to Tunis-Carthage International Airport on Tuesday night to take his flight to the United States. But he was not allowed to travel because US authorities had rejected his entrance visa.
Morro reportedly said he was "surprised" by the move, for he had regularly visited the country over the last three years to attend conferences organised by Muslim Americans supporting the Palestinian cause.
A number of Ennahda leaders have been put on the US entrance-ban list, Tunisia's Al-Sherouq newspaper reported.
Morro has been proposed as the next speaker in the recently elected parliament.
October's parliamentary vote saw secular Nidaa Tounes gain 85 seats (38.24 percent) in the 217-seat assembly, while the Islamist Ennahda movement came in second with 68 seats (31.33 percent).
Ennahda's consultative council will meet on Saturday to discuss the party's choices in the upcoming presidential run-off.
In the first round of voting, Nidaa leader Beji Caid Essebsi earned roughly 42 percent of the votes, Moncef Marzouki came second with about 22 percent, while Hamma Al-Hammai - a leftist candidate - came third with 10 percent.