If a joint owner of a bank account spends a significant portion of money without the other’s permission and doesn’t ascribe ownership of the purchases to the other parties, what are the legal and non-legal remedies available?
In most cases, there is no direct legal recourse for such a withdrawal. Money in a joint account is co-owned, and any account holder may withdraw any of it for any lawful purpose.
As the article "What is a joint bank account?" from Bankrate.com states:
The money in joint accounts belongs to both owners. Either person can withdraw or spend the money at will — even if they weren’t the one to deposit the funds. The bank makes no distinction between money deposited by one person or the other, making a joint account useful for handling shared expenses. But a joint bank account should only be opened with someone whom you trust, since that person has equal control over the account’s funds.
If the account holders have a contract or legal agreement that controls what money can be withdrawn and for what purposes, then a violation of such an agreement might be a cause for legal action. But merely opening a joint account does not create such an agreement nor imply it.
It would depend heavily on your juresdiction and what the relationship between the account holders was.
For example, if the account is owned by a married couple in a state/country with community property laws then there would likely be no criminal or civil recourse unless the money was withdrawn under false pretenses. In which case fraud laws "may" be applicable.
As a rule of thumb, I would say that no action could be taken immediately, through the existence of the withdrawal might be a factor in the division of property after a divorce.