My wife is thinking about getting another job and taking a 50% pay cut and I don't want her to.
Are you worried that she might leave you?
No, it's because I will be unable to trust her thereafter.
You shouldn't be trying to control you spouses finances. You come across as very controlling and that's not something that will lead to a healthy relationship. If you think that you're having issues trust your partner you should think about talking to them about it.
What is wrong with marrying a woman who you don't trust?
Well, marrying a woman you don't trust is wrong because that means you'll constantly have issues like this one where you're attempting to now control her finances. Trust is how you keep a marriage together for a very long time with no worry about divorce, so you really should work on that.