need client permission for engage in investment consulting outside the firm?

it is from a question in Qbank, which says it is correct to “receive permission from both their employer and outside clients to engage in investment consulting outside the firm.” I thought just disclosure is needed, why permission? you only need permission from employer that is what I think, correct? Thanks.

I think because it is related to investment consulting which is similar to his full-time job. If he wants to become a director of some public school - he will have to disclose to both the parties but will need permission only from his employer.