I doubt that is the main reason for the departure because, imo, the internal policy requirement to surrender other sources of income earned by employees of the audit firm are for quality control purposes, to help remove threats to independence in appearance and mind. From my googling

, there is no such guideline in the international or local auditing standards to make it compulsory to surrender such other sources of income. Imo, such requirements can be waived, as long as there is no conflict of interest.
www.ifac.org/auditing-assurance
www.icpascaa.org.sg/standards/ssa
Not being trained in financial matters, at the most, doing assurance work on non financial related areas. Many still do not understand what an "associate" means in an audit firm because fingers are too lay at the keyboard to even google a query when in doubt.
Imo, the main reason (as another forumer has also posted sometime back) is that the job position held in the true private sector which is most aspects subjected to real market forces, reflects an individuals capabilities, which is in this context, may be perceived as not befitting the political station, following public opinion during the GE. Since there is peer competition and appraisals, any movement upwards would cause an uproar and discontentment within the industry.
My guess; spin doctors came up with a idea with the object to achieve a win win situation, in the hope to create an impression of dedication and committment to current task through resignation.............and so they thought:o
Everyone thinks that Tin Pei Ling is very concerned about her
residents in Macpherson to quit her job in Ernst & Young to serve as a
full-time MP.
There is a human resource policy in Ernst & Young and the other big 4
audit companies (PwC, KPMG Ernst & Young, Deloitte Touch Tohmatsu)
that if any of its employees were to earn an allowance or income from
any other source, they would have to surrender this amount to the HR
department.
The salary for Tin Pei Ling as a recently promoted senior associate at
Associate at Ernst & Young will be no more than $8000. Whereas as an
MP she earns $16000. If she did not resign from Ernst & Young, she
would have to surrender this $16000 (which is more than 2 times the
salary she earns at Ernst & Young) to the company's HR department and
they would donate it to a charity of her choosing.
So you see.... Tin Pei Ling's reason for resigning is not so noble
after all. She just wants to make more money as an MP, which she
cannot do if she were to remain at Ernst & Young. If she is not
re-elected in the next General Election, I wonder who will employ
someone like Tin Pei Ling and give her a $16000 salary. Only Prime
Minister Lee Hsien Loong is so generous.