The California State Teachers’ Retirement System, the largest teachers’ retirement fund in the country and known as CalSTRS, filed an important lawsuit this month against 27 current and past executives and directors of Wal-Mart Stores Inc., the world’s largest employer.
The case alleges widespread corruption and bribery at the company’s Mexican subsidiary. Last week, the company said it was expanding an internal inquiry to include other subsidiaries. The Justice Department and the Securities and Exchange Commission have begun parallel inquiries. This suit, along with those investigations, could help ensure that the company reckons with what it did wrong and fixes its broken corporate governance.
http://www.nytimes.com/2012/05/22/opinion/the-wal-mart-corruption-case.html?nl=todaysheadlines&emc=edit_th_20120522
Of course if they really wanted to get Wal Mart's attention, they could simply divest themselves of those stock holdings. 
