Or: ...shall be exercised on your own initiative
Or: ....shall be exercised of one's own accord


--- The verb "行使する" is about exercising (one's) rights

Here are some examples:
http://ejje.weblio.jp/content/権利を行使する
権利を行使する
to exercise the right
権利を行使する
exercise [abuse] one's rights

http://ejje.weblio.jp/content/否認権の行使
法令用語日英標準対訳辞書
否認権の行使
exercise of right of avoidance

Without more context, I can only be so helpful. However, it seems to me that the "自ら" here is not meant to refer to the initiative of the actor, given that this is about exercising power/authority (権限) rather than rights in the "individual-vs-entity" sense. In other words, I don't think that "権限の行使" is supposed to be optional.

I think the author is trying to say something similar (but not identical) to the following:

http://www.wvlottery.com/videolottery/hb102.aspx
§29-22B-401. General authority of state lottery commission and director; conflicts.
(a) The lottery commission created by section 29-22-4 of this code is authorized to implement and operate a system of limited video lottery in accordance with the provisions of this article and the applicable provisions of article 22 of this chapter.
(b) The state lottery commission and the director of the commission shall exercise their respective powers and perform their respective duties and functions as specified in this article.

http://www.gofhspanthers.org/FHS Booster Club ByLaws.htm
The affairs of the organization shall be determined by the membership, and by majority vote, with the day-to-day affairs being conducted by the officers and directors in accordance with their duties as hereinafter specified.

http://210.75.211.75:81/capinfo/html/info/1011011433095358.h...
The departments of public security, procurator, justice, industrial and commercial administration, quality and technical supervision, etc. at various levels in this Municipality shall, according to law and in accordance with their respective duties and responsibilities, maintain the order of power-supply and use and protect the lawful rights and interests of power-supply enterprises and consumers.

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Note added at 14 hrs (2011-02-27 02:38:37 GMT)
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From the Japanese constitution:
http://www.constitution.org/cons/japan.txt
第８３条
国の財政を処理する権限は、国会の議決に基いて、これを行使しなければならない。
Article 83.
The power to administer national finances shall be exercised as the Diet shall determine.

From the Swedish constitution:
http://www.servat.unibe.ch/icl/sw00000_.html
Article 1
(1) All public power in Sweden proceeds from the people.
(2) Swedish democracy is founded on freedom of opinion and on universal and equal suffrage. It shall be realized through a representative and parliamentary polity and through local self-government.
(3) Public power shall be exercised under the law.

http://souansyuu.exblog.jp/i17/
スウェーデン統治法典　第一章　第１条　〔主権〕
１　すべての公権力は、国民から発する。
２　スウェーデン民主主義は、言論の自由と普通平等選挙権に基づき、代表制議会主義と地方自治を通じて実現されなければならない。
３　公権力は、法律に基づいて行使しなければならない。