In a Catholic Culture summary:

Bishop Thomas Tobin of Providence has issued a strong statement lamenting the passage of legislation allowing for civil unions in Rhode Island, and warned Catholics that they cannot be involved in such unions.

The legal acceptance of civil unions, the outspoken bishop said, involves “a social experiment that promotes an immoral lifestyle, is a mockery of the institution of marriage as designed by God, undermines the well-being of our families, and poses a threat to religious liberty.”

After reaffirming the Church’s teaching that homosexual activity is gravely sinful, Bishop Tobin instructed the faithful not to be a part of civil unions:

Because civil unions promote an unacceptable lifestyle, undermine the faith of the Church on holy matrimony, and cause scandal and confusion, Catholics may not participate in civil unions. To do so is a very grave violation of the moral law and, thus, seriously sinful. A civil union can never be accepted as a legitimate alternative to matrimony.