The Bishops got all into Social Justice in the 80's, pushed largely by their liberal staff members and feminist nuns who'd decided that just teaching children and nursing weren't enough for their liberated selves, so they wanted to be full fledged social workers, and create a 'preferential option for the poor' within the Church. In their zeal, and stupidity, they even crossed over into helping fund groups that pushed for abortion.
Immigration is one of those issues about which Catholics can disagree with their Bishops, and still be within the teachings of the Church, because it's not one of the more morally fundamental issues like abortion.