The new laws in Europe, and soon to be in Great Britain, concerning civil marriages for "gays" will not only affect teachers and registrars who may have to leave their jobs, but the very institution of Catholic marriage.
Catholics "marry" twice-one getting a civil marriage license, or registrar's "marriage" and the sacrament of Matrimony. The Church may be forced into a position wherein she no longer can accept civil unions at all. Why?
To avoid any sham sacramental marriage, the Church may have to reject civil marriages across the board.
What this would mean for Catholic sacramental marriages could be a series of losses of marriage legal status, rights, tax breaks, allowances, etc.
I think Catholic marriages will be forced to go underground 0r without legal definition or legal protection. One of the possibilities, that once civil unions are legal, the Catholic Church will have to leave the business of accepting civil status and only accept sacramental status. In other words, the Church may be put in a position where she only recognizes sacramental marriages, which means, that Catholic married couples will be seen by the State as merely living in concubinage and therefore, without any civil or tax rights.
This has already happened here, in England under the persecutions, when Catholic marriages were not seen as valid by the State, as only Anglican ones were. I predict this will happen both in America and in England, as the only way the Church will be able to avoid gay marriages. That is, no civil involvement at all.
Therefore, Catholic married people will not be recognized by the State as married and will not benefit from marriage tax breaks, etc. If you do not think this is a possibility, I suggest a careful reading of the history of marriage in England. Before 1836, everyone except Jews and Quakers had to get an Anglican license, that is, be married in the Anglican Church in order to be recognized. See the pattern? Parliament decides the process, not the churches. Also, after 1836, with the new registry laws, the license costs as much as 250 pound sterling in today's money, which would have been very difficult for some people, including Catholics. Here is a short quotation from a site here which is not exhaustive but interesting.