An organisation representing LGBT Catholics around the world has been denied permission for a stall at the World Meeting of Families in Dublin, which Pope Francis is attending on 25 August.

The Global Network of Rainbow Catholics, which represents 60 organisations, has been told that “logistical considerations” and uncertainty regarding the amount of space available mean that it has not been allocated a booth in the gathering’s exhibition hall.

The WMF, an international event held by the Roman Catholic church every three years, opens in Dublin next Monday. Pope Francis will spend 36 hours in Ireland attending events and celebrating masses.

The GNRC applied to be allocated a stall at the exhibition hall in April. Despite repeated queries about the progress of its application, it was told only in the past few days that it had been rejected.

Ruby Almeida, a co-chair of the GNRC, said she was saddened and frustrated by the decision. “I think it’s the usual thing that goes on – the church publicly says it’s welcoming [to LGBT people and organisations] but pressure is brought to bear on the organisers. We wanted to be able to go and say this is who we are, let’s have a conversation.”

Although the pope was “trying to create space for us”, there were conservative forces in the Vatican holding sway, she said. “There’s a huge power struggle going on in the Vatican, but people want to see change. They’re fighting a losing battle.”

According to the GNRC, Paul McCann, the exhibition coordinator for WMF, said the application had been unsuccessful because of “uncertainties over the amount of space we will have available for exhibitions because of other logistical considerations”.

Another organisation, We Are Church, which campaigns for equality and inclusivity within the Catholic church, has also been denied permission for a stall in the exhibition hall.

The WMF had shown “a closed and exclusive mentality which contradicts Pope Francis’s constant calls for dialogue in the Catholic church,” Brendan Butler, the Ireland spokesperson for We Are Church, told the Irish Times last month.

Diarmuid Martin, the archbishop of Dublin, has said the WMF welcomes everyone, despite the replacement of five pictures of same-sex couples with traditional families in WMF leaflets in January.

In addition, a video by David O’Connell, the auxiliary bishop of Los Angeles, was edited to remove his statement that all families, including gay families, were welcome at the event.

However, the gathering will be addressed by Father James Martin, an American Jesuit priest and vocal advocate for LGBT rights.

The Irish Society for Christian Civilisation is appealing for signatories to a petition urging Archbishop Martin to disinvite Fr Martin, arguing that he is “well known for his dissent from church teaching on sexual morality” and that any address will “cast a shadow” over the WMF. Nearly 11,000 people have backed the petition.

Leo Varadkar, the Irish taoiseach, has said he will raise the issue of same-sex marriage and LGBT rights with the pope when he meets him next weekend.

Three years ago Ireland voted in a referendum to back same sex-marriage, defying the teaching of the Catholic church and becoming the first country in the world to endorse marriage equality in a popular vote.

The WMF has not responded to a request for comment from the Guardian.