DUBLIN — The Irish nationalist Sinn Féin party has expelled a member over her possible link to a conspiracy to bomb a mosque — and stressed it won’t tolerate far-right racists in its ranks.

Sinn Féin, Ireland’s main opposition party, confirmed the expulsion Thursday hours after the party member’s partner was arrested on suspicion of involvement in an alleged plot to attack immigrants.

Sinn Féin declined to identify the woman or her partner, but confirmed both of them last year had been guests of the party inside Ireland’s parliament building, Leinster House.

The episode underscores how immigration has become a particularly tricky issue for Sinn Féin. Rising tension over immigration has sparked occasional rioting in Ireland, which a generation ago was virtually all-white but today has more than 1 million foreign-born residents in its 5.4 million population.

Sinn Féin bills itself as a party of the left. Its leaders are traditionally pro-immigrant and have made support for the Palestinian cause a core issue. But surveys have found that many grassroots members take a hostile view of immigrants, particularly from Africa and predominantly Muslim nations.

Sinn Féin confirmed it expelled the member on Saturday, a day after anti-terrorist police raided her and her partner’s home in County Laois in Ireland’s rural midlands.

“We will not allow our party to be exposed to any far-right elements,” Sinn Féin chairman Declan Kearney said in a statement. “The far right have targeted our party for several years now with death threats, pickets on members’ homes and offices and, more recently, violent actions.”

Police suspect that the County Laois home may have been used to film a propaganda video by a new terrorist group styling itself as the Irish Defence Army.

In that video, seized by police last week, four men wearing balaclavas spoke in front of an Irish flag. Their message, as detailed in an accompanying manifesto discovered by police, included threats to bomb the mosque in the western city of Galway and to attack shelters housing asylum-seekers.

Two men whom police have linked to the video already have been charged with possession of explosives: Garrett Pollock, 35, from Annalong in the neighboring U.K. territory of Northern Ireland; and  Karolis Peckauskas, a 38-year-old engineer from Lithuania living in the Irish town of Drogheda.

The expelled Sinn Féin activist’s partner was arrested at their Laois home Wednesday night and is still being questioned.

Such police raids on Sinn Féin activists’ homes were once everyday occurrences but are rare today, given the party’s stunning pivot away from its bloody past.

The modern Sinn Féin party was founded in 1970 in Belfast as part of a breakaway movement in the early days of Northern Ireland’s conflict. It long served as the face of an outlawed group, the Provisional Irish Republican Army, that killed nearly 1,800 people during a 27-year campaign of bombings and shootings.

Once the Provisional IRA stopped its attacks in 1997 and disarmed eight years later, Sinn Féin’s support surged on both sides of the Irish border. In the north, Sinn Féin leads its cross-community government. In the south, the party has gone from having no lawmakers before the IRA cease-fire to 39 today in Dáil Éireann, Ireland’s 174-seat parliament.

With the passage of time, fewer of today’s Sinn Féin activists have paramilitary backgrounds. Party leader Mary Lou McDonald, for example, joined Sinn Féin after the IRA laid down its weapons.