What is the salary for US Supreme Court justices?

According to the US Code regarding Ethics, Title 5A, §501, career government employees who occupy positions above GS-15 (which includes all US Supreme Court justices) have an outside earned income cap equal to 15% or less of their annual salary. They may not accept money for speaking engagements (called Honoraria, see (b)) other than reimbursement of reasonable expenses. The institution to which they speak may, instead, donate a maximum of $2,000 to a charity on the speaker's behalf.

Retired justices, on the other hand, sometimes command six-figure fees for a single key-note address.

Ethics, Title 5A, §501

(a) Outside Earned Income Limitation.-

(1) Except as provided by paragraph (2), a Member or an officer or employee who is a noncareer officer or employee and who occupies a position classified above GS-15 of the General Schedule or, in the case of positions not under the General Schedule, for which the rate of basic pay is equal to or greater than 120 percent of the minimum rate of basic pay payable for GS-15 of the General Schedule, may not in any calendar year have outside earned income attributable to such calendar year which exceeds 15 percent of the annual rate of basic pay for level II of the Executive Schedule under section 5313 of title 5, United States Code, as of January 1 of such calendar year.

(2) In the case of any individual who during a calendar year becomes a Member or an officer or employee who is a noncareer officer or employee and who occupies a position classified above GS-15 of the General Schedule or, in the case of positions not under the General Schedule, for which the rate of basic pay is equal to or greater than 120 percent of the minimum rate of basic pay payable for GS-15 of the General Schedule, such individual may not have outside earned income attributable to the portion of that calendar year which occurs after such individual becomes a Member or such an officer or employee which exceeds 15 percent of the annual rate of basic pay for level II of the Executive Schedule under section 5313 of title 5, United States Code, as of January 1 of such calendar year multiplied by a fraction the numerator of which is the number of days such individual is a Member or such officer or employee during such calendar year and the denominator of which is 365.

(b) Honoraria Prohibition.- An individual may not receive any honorarium while that individual is a Member, officer or employee.

(c) Treatment of Charitable Contributions.- Any honorarium which, except for subsection (b), might be paid to a Member, officer or employee, but which is paid instead on behalf of such Member, officer or employee to a charitable organization, shall be deemed not to be received by such Member, officer or employee. No such payment shall exceed $2,000 or be made to a charitable organization from which such individual or a parent, sibling, spouse, child, or dependent relative of such individual derives any financial benefit.