Nowhere the rule says that after getting Green Card, a person has to stay in the same company through which the Green card was processed.
INS says the following about naturalization:
Naturalization is the process by which U.S. citizenship is conferred upon a foreign citizen or national after he or she fulfills the requirements established by Congress in the Immigration and Nationality Act (INA). The general requirements for administrative naturalization include:
* a period of continuous residence and physical presence in the United States;
* residence in a particular INS District prior to filing;
* an ability to read, write and speak English;
* a knowledge and understanding of U.S. history and government;
* good moral character;
* attachment to the principles of the U.S. Constitution; and,
* favorable disposition toward the United States.
All naturalization applicants must demonstrate good moral character, attachment, and favorable disposition.
Visit
http://www.ins.gov/graphics/services/natz/index.htm for details.