Is one allowed to borrow money from a credit union?
One is not allowed to borrow from a credit union if it has Jewish members. A credit union is not like regular banks in the diaspora.
Many credit unions in the United States have at least one Jewish member, therefore one may not borrow from any credit union unless it was ascertained that there are no Jewish members or that there was a Kosher Heter Iska contract formed.
Even if a Heter Iska was formed, there would be a problem with collecting interest returns, unless every Jewish member arranged a kosher Heter Iska.
Reasoning:
See Shulchan Aruch Admur Hazaken Hilchos Ribis Vi’Hilchos Iska 4-5 where it explains that any exchange of paying extra in place of receiving a loan is ribbis, similar to the concept of ‘renting money’.
Regarding banks in the diaspora, there is a debate in the Poskim as to what amount of Jewish ownership would be considered forbidden to borrow from the bank. See Bris Yehuda chapter 30 footnote 43. Some Poskim hold that if the majority of the bank shares/ownership is held by non-Jews, it would be permissible to borrow from a bank. Igros Moshe (Even Haezer 1:7 ד”ה ובדבר) is of the view that even if a single Jew has a significant ownership percentage of the bank, in which he has executive decision rights as being a voting board member it would be forbidden to borrow from such a bank, however mere stockholders do not pose any real ownership rights.
However, the Poskim explain that banks is a more complex system since they sell stock shares which therefore there are certain leniencies.
However, a credit union is just a simple partnership between its members, therefore even if there is even a minute amount of Jews, it would be a problem of Ribbis. See also Birchos Aryeh page 48.
See also references here:
#9233