The May 30th Movement
Following the establishment of the first KMT-CPC cooperation, the CPC continued to lead the workers' movement nationwide. On May 1, 1925, the All-China Federation of Trade Unions was founded in Guangzhou, and CPC members Lin Weimin (1887-1927) and Liu Shaoqi (1898-1969) were elected president and vice president.
On May 15, the Japanese owner of a cotton mill in Shanghai shot dead Gu Zhenghong (1905-1925), a CPC member and workers leader, and wounded a dozen others. The CPC Central Committee decided to mobilize the local people to stage an anti-imperialist demonstration in the International Settlement. On May 30, as the workers and students protested in the street in support of the textile workers, the British police suddenly opened fire on the Nanjing Road, killing 13 and wounding many others. This was known as the May 30th Massacre. In the days after, there were incidents of British and Japanese police killing Chinese civilians in Shanghai and other cities.
The massacres enraged the whole nation. The CPC Central Committee decided to set up an action committee composed of Qu Qiubai, Cai Hesen, Li Lisan, Liu Shaoqi and Liu Hua (1899-1925) to organize demonstrations and strikes by workers, students and shopkeepers in Shanghai. Under the CPC's leadership, the May 30th Movement swept the whole country, and about 17 million people from all walks of life participated, forming a tremendous anti-imperialist movement with an international impact.
The CPC's influence was reinforced during the May 30th Movement, and its membership increased tenfold within a year. The movement directly led to the general strikes in Guangzhou and Hong Kong, which lasted for 16 months with 250,000 participants and sparked a further upsurge of revolution across China.
五卅运动
第一次国共合作建立后，中国共产党继续领导全国的工人和群众运动。1925年5月1日，中华全国总工会在广州正式成立，共产党员林伟民、刘少奇分别当选为正、副委员长。5月15日，上海内外棉七厂的日本资本家枪杀工人代表、共产党员顾正红，打伤工人10余人。中共中央决定在租界内举行大规模的反帝示威活动。5月30日，上海工人和学生举行街头宣传和示威游行，租界的英国巡捕在南京路上突然开枪，打死13人，伤者不计其数，制造了震惊全国的五卅惨案。此后几天，在上海和其他地方又连续发生英、日等国军警枪杀中国人的事件。
这些事件，激起了全国人民的极大愤怒。中共中央决定由瞿秋白、蔡和森、李立三、刘少奇和刘华等组成行动委员会，组织全上海工人罢工、学生罢课、商人罢市的抗议运动。在中国共产党的领导和推动下，五卅运动迅速席卷全国，约有1700万人直接参加了运动，形成了全国规模的反帝怒潮和具有广泛国际影响的反帝斗争。
五卅运动扩大了中国共产党在全国的影响，党员数量一年内增加了10倍。这一运动直接推动了历时16个月、25万人参加的省港大罢工的兴起，对大革命高潮的形成起到重要的推动作用。