Rav Moshe Sternbuch (5:327): The poskim have much discussion about the issue of civil marriage because the matter is complicated and deals with the issue of a married woman which is amongst the most severe prohibitions. There are many different aspects and questions. A look at the writings of recent poskim will see that there is no general psak in this matter because the actual halacha varies depending upon place and time and the couple involved. Therefore it is necessary to investigate carefully every single case with calm deliberation and the final halacha is given to the authority of beis din or at least to the gedolim.
The fact is that it is accepted practice today that a couple who have a civil marriage require a get when possible. However in difficult circumstances when it is impossible to obtain a get the practice is to permit remarriage without a get. And surely this is true if she is remarried already without a get and has a child – that the child is not considered a mamzer. And this is what Rav Chaim Ozer (Igros Rav Chaim Ozer #30) has written that one can rely on the great poskim such as Maharam Shick (#21), Beis Yitzchok (#29), Beis Ephraim (#41) to permit the woman to remarry – in time of need – without a get. However it is important to know that there are also gedolim that are machmir in this matter, See Even Haezel (Rav Issur Zalman Meltzer) who discusses this a great length (Chapter 6 Hilchos Ishus). He concludes, “In conclusion, kiddushin from another person after previously living together as man and wife is the severe prohibition of adultery. Therefore one should not make halachic rulings that permit this even by combining various leniencies to nullify kiddushin after a couple has been living together. Anyone who insists on being lenient in these circumstances – makes absolutely no sense and he requires atonement for his errors in deciding halacha concerning a prohibition that involves capital punishment and mamzerim and he must correct what has been done.” In sum he writes very strongly that one should not permit remarriage without a get. We find a similar view expressed by Ohr Someach (Hilchos Geirushin 10:19) who shows that the principle that a person doesn’t have sexual intercourse without marriage is not because of a prohibition but because living with a woman shows that he wants her to be his wife and thus they are halachically married.
However their words seem astounding. It is obvious that if a person gets a civil marriage and not a religious one – he is clearly indicating that he has no interest in a religious marriage. So how can you claim that such a person should be considered married according to Jew law? This is not equivalent to someone who gets married with less that a peruta – because that at least shows he wants to be married according to the Torah. If so then when he has sexual relations with his wife afterwards that finalizes the status of marriage according to the halacha. In contrast when he clearly indicates that he has no interest in a Jewish marriage. Elsewhere (2:642) that basis for concern that civil marriage might be valid is according to the view of Rav Huna that chuppah acquires in marriage (Kiddushin 5a). Rabbeinu Chananel rules according to Rav Huna’s view. In Shulchan Aruch (E.H. 26:2) he writes as minority opinion that if one brings a women into chuppah there is a question as to whether it is valid. Therefore we might say that by taking a woman into his house for the sake of marriage there is a concern that they are married. However this can be answered by saying that it is true if they wanted a valid marriage according to the Torah. However if he only had a civil marriage – that shows that he doesn’t want a religious marriage and therefore the kiddushin has no validity.
All of the discussion so far only applies to a civil marriage, but if they want a religious ceremony but they decided to have a Reform marriage because they have been misled into thinking that Reform also provide a religious marriage and they think that the Chareidim are just being strict and exaggerate the importance of their ceremony. They simply don’t understand that the Reform have cut themselves off totally from the Jewish religion. If that is what they are thinking then in truth their intent is to have a genuine religious marriage and then it would seem that the Reform ceremoney would be valid since there is the principle that , “ A person doesn’t have intercourse outside of a genuine marriage.” However that is not clear because the Rambam (Hilchos Ishus 7) writes, “There is a presumption that a religious Jew would not have intercourse outside of marriage when he has the opportunity to be married.” Obviously this principle does not applies to those who reject G‑d’s mitzvos. Along with this problem the validity of a Refom marriage is undermined by the lack of valid witnesses and questions regarding the nature of kiddushin they perform and the presumption of virginity. Consequently my view is that if the couple remarried without first obtaining a Get it is possible to be lenient regarding the doubt regarding mamzerim which in this case is only rabbinic. However to permit them to remarry without a get – I believe it is necessary to distingush between civil marriage and Reform marriage. While a civil marriage does require l’chatchila a Get however it is possible to allow them to get remarried without a Get when it is of great necessity. In contrast a Reform marriage in which they intended to be married according to religion but they were mistaken – then the obligation to obtain a Get is much greater. Therefore it is possible to allow remarriage without a Get in such a case - only when it would result in the woman remaining unmarriable. In such a case the permission to remarry must be made by beis din. In another place, I mention that in a situation where there is a dispute amongst poskim and a heter is needed - e.g., a marriage which was done not in accord to Torah law – than it is proper to receive permssion to remarry from beis din or at least three major rabbis.