Sinn Féin's representative to Washington, Rita O'Hare, has been denied permission by the State Department to visit the United States next week. Conor O'Clery reports from New York
However, a State Department spokesman in Washington said this did not represent a change in policy towards Sinn Féin.
It is also understood from official sources that the ban is temporary.
Sinn Féin MP Martin McGuinness has been given permission to travel to New York and Washington next week and he is expected to meet State Department officials in the US capital.
Ms O'Hare, a frequent visitor to the US, planned to accompany Mr McGuinness, but was refused permission, apparently as "punishment" for deviating from her agreed itinerary on a recent visit to the US.
Like many Sinn Féin figures, Ms O'Hare is ineligible for a US visa because of her past association with the IRA and must apply for a waiver for each visit. A waiver has been granted regularly in the last six years, allowing Ms O'Hare to make frequent visits to the US as Sinn Féin's Washington representative.
One of the rules of the waiver is that the person applying must provide a detailed itinerary, giving details of what places are to be visited in the US.
It is understood that on a recent visit with Sinn Féin negotiator Gerry Kelly, Ms O'Hare notified the State Department of her intention to visit New York, where she had arranged to meet Bill Flynn, chairman of Mutual of America and a major supporter of the peace process.
However, Mr Flynn was in Florida and the Sinn Féin representative flew to see him there, though it was not on her official itinerary.
The action of the State Department is being interpreted by some Irish-Americans as a shot across the bows for Sinn Féin, while Washington awaits the IRA's response to Gerry Adams's call to the IRA to engage in purely political and democratic activity.
The State Department said its position is unchanged in that it attaches importance to the peace process, and continued dialogue with Sinn Féin is part of that.
"There is no change of policy," a State Department spokesman said, while declining to discuss an individual visa application.
It has been the policy of the US administration to grant waivers to Sinn Féin representatives to visit the US to facilitate the dialogue.