In the Extraordinary Shareholder Meeting held on September 30, 2012, a Voluntary Share Conversion Plan was created to convert class A shares into class B shares. This plan was created in case the class A shares were to lose liquidity in the market, the class A shareholders would have the option to convert their shares into class B shares, on a 1:1 ratio (one class A share for one class B share).
In accordance with what was approved at that time, the voluntary share conversion plan will finalize on December 31, 2017. After such date, both share classes will continue to trade and be listed, but the conversion plan will cease to exist. In order to convert your shares into class B shares, you would need to give the specific instruction to your custodian entity (if you don't give the specific order, you will maintain your class A shares). Under no circumstance can your shares be converted automatically or without your instruction, unless a different plan is otherwise approved in a future shareholder meeting.
For more information please see the following Material Fact published on December 4, 2017:
Ordinary General Shareholders' Meeting 2017