Read this and answer the question. If the question is unanswerable, say "unanswerable".

Foxconn, Apple's manufacturer, initially denied the abuses, but when an auditing team from Apple found that workers had been working longer hours than were allowed under Chinese law, they promised to prevent workers working more hours than the code allowed. Apple hired a workplace standards auditing company, Verité, and joined the Electronic Industry Code of Conduct Implementation Group to oversee the measures. On December 31, 2006, workers at the Foxconn factory in Longhua, Shenzhen formed a union affiliated with the All-China Federation of Trade Unions, the Chinese government-approved union umbrella organization.

In what year did Foxconn workers first unionize?
2006