The CSSTA, or Cross-Strait Services Trade Agreement (海峽兩岸服務貿易協議 frequently abbreviated to 服貿), was a free trade agreement that was to be signed with China by the Ma administration. This was to be conducted through the Chinese and Taiwanese intermediary organizations of the Association for Relations Across the Taiwan Straits and the Straits Exchange Foundation, respectively.
Critics of the Sunflower Movement often claim that opposition to the CSSTA was irrational. The CSSTA was opposed by Sunflower Movement demonstrators merely because of the fact that it was a trade agreement to be signed with China. And so the claim went that Sunflower Movement was merely symptomatic of conflicted anger over identity.
Yet fear about the CSSTA does not seem unwarranted. The agreement would allow for Chinese dominance of Taiwan’s economy and, in that way, allow for eventual Chinese political control of Taiwan. Namely, the CSSTA would have opened up 64 sectors of the Taiwanese economy to Chinese investment, as well as opening up 80 sectors of the Chinese economy to Taiwanese investment. Moreover, the service industry comprises the majority of the Taiwanese economy, comprising more than 70% of the Taiwanese economy.
Indeed, it is obvious that the Chinese economy is that much larger than the Taiwanese economy and so this would have affected the Taiwanese economy far more than the Chinese economy. Sectors of the economy ranging from the business sector to the healthcare industry to environmental services, social services, financial services, engineering services, and cultural services would have been affected.
In this light, alarm over the CSSTA seems wholly justified. China, after all, has a long history of attempting to use the economy as a weapon against its enemies, and this seems likely to be no different with Taiwan. As a result, resistance to the CSSTA began among Taiwanese student activists in 2013, with demonstrations particularly fronted by the Black Island Youth Front. 
Read More About The Demands Of The Movement:
 Chen Ling 陳玲. Dangqian xingshi xia de taiwan xue yun yanjiu 當前形勢下的臺灣學運研究. Shi ying chuban she 時英出版社, Taipei (2015). Print. P. 1.