They are urging the UK to think about the political, economic and cultural implications for Ireland and Northern Ireland if an exit European Union (EU) vote wins.
The bishops have released a statement that reads: "The reintroduction of border controls, for example, would not only have profound implications for trade and the economy, but also for the wider civil society, notably through the disruptive impact on the
day-to-day life of those who live in border areas or cross the border frequently.
"The valuable work carried out to date to build new relationships across these islands must not be undermined."
The group praises the work the EU has undertaken in the search for peace and reconciliation in the region.
The statement says EU efforts are evident in "many ways, including the creation of important spaces for dialogue, financial support for the work of peace and reconciliation, freedom of movement of people, and the development of infrastructure to support new relationships across the island of Ireland and with the UK."
It stresses that voters "need to be cautious about arguments that would reduce the wide ranging benefits of EU membership to a single calculation of net economic gain or loss."
The bishops warn that an exit vote could possibly mean the reintroduction of border controls between the two countries.
They said this "would not only have profound implications for trade and the economy, but also for the wider civil society, notably through the disruptive impact on the day-to-day life of those who live in border areas or cross the border frequently.
"The valuable work carried out to date to build new relationships across these islands must not be undermined."
Leave campaigners argue that being in the EU makes it easier for terrorists to come to the UK and say the supremacy of EU courts makes it harder to deport violent criminals.
It also says membership costs £350m a week and if the UK left, billions of pounds would become available for other projects.
