"Especially since all the employment contracts I've seen have had clauses that say the salary and all remuneration is confidential."

Lets assume that you have signed an agreement to not tell anybody what your income is. Taken to the extreme that would mean that your can't apply for a car loan, or a mortgage, or a credit card. All these things require you to tell them your income so that they can determine if your can afford it. Also your bank and the IRS know. Lenders sometimes require you to submit copies of tax forms, or pay stubs.

So why does your broker need to know? If you are wanting to invest in complicated markets they need to know your can afford the amount your are risking. If your are purchasing investment advice they also need to understand your entire financial situation before suggesting specific investments.

"Especially since all the employment contracts I've seen have had clauses that say the salary and all remuneration is confidential."

Let's assume that you have signed an agreement to not tell anybody what your income is. Taken to the extreme that would mean that you can't apply for a car loan, or a mortgage, or a credit card. All these things require you to tell them your income so that they can determine if you can afford it. Also your bank and the IRS know. Lenders sometimes require you to submit copies of tax forms, or pay stubs.

So why does your broker need to know? If you are wanting to invest in complicated markets they need to know you can afford the amount you are risking. If you are purchasing investment advice they also need to understand your entire financial situation before suggesting specific investments.