The quotation is from Mao's Report at the Second Plenary Session of the 7th Central Committee of the CCP (在中国共产党第七届中央委员会第二次全体会议上的报告 - Zai Zhongguo gongchandang diqijie zhongyang weiyuanhui di'erci quanti huiyi shangde baogao.
One of the worker holds a volume of the "Selected Works of Mao Zedong" (毛泽东选集 - Mao Zedong xuanji).