Key language in the letter from the bishops:

"We recognize that the law has brought about important gains in coverage, and those gains should be protected. The Catholic bishops of the United States will examine health care proposals in greater depth and from various perspectives in the days ahead. But we note for now that a repeal of key provisions of the Affordable Care Act ought not be undertaken without the concurrent passage of a replacement plan that ensures access to adequate health care for the millions of people who now rely upon it for their wellbeing. Particularly for those who would otherwise be required to use limited resources to meet basic needs such as food and shelter rather than seek medical care, the introduction of great uncertainty at this time would prove particularly devastating"

The whole letter to congress: http://www.usccb.org/issues-and-action/human-life-and-dignity/health-care/upload/letter-to-congress-from-bishop-dewane-re-aca-2017-01-18.pdf