48 But in matters merely political, as, for instance, the best form of government, and this or that system of administration, a difference of opinion is lawful. Those, therefore, whose piety is in other respects known, and whose minds are ready to accept in all obedience the decrees of the apostolic see, cannot in justice be accounted as bad men because they disagree as to subjects We have mentioned; and still graver wrong will be done them, if - as We have more than once perceived with regret - they are accused of violating, or of wavering in, the Catholic faith.
Source: Immortale Dei (Vatican.va)