On the one hand, students from the TSPM seminaries in the cities of Nanjing, Shanghai, and Beijing demonstrated in favor of political reform (see Tony Lambert, The Resurrection of the Chinese Church, pp. 214-215). Even the leader of the TSPM, Bishop Ding Guangxun, who was closely connected to the Chinese government, issued statements in support of the student demonstrators in Beijing.
On the other hand, according to Tony Lambert, a former British diplomat in China and a long-time observer of Christianity in that country, "the house-church Christians, as far as is known, largely stood aside from the democracy movement" (The Resurrection of the Chinese Church, p. 218).
It might seem paradoxical that Christians associated with the government-controlled TSPM should protest against the Chinese government, while believers in churches not sanctioned by the government--who were, in effect, "dissidents" due to their refusal to accept government control--did not. However, there are actually good reasons for this seeming paradox. On the one hand, the TSPM at the time was closely linked to the reformist wing within the ruling Chinese Communist Party. Thus, reformists within the Party itself may have encouraged--or at least, were not inclined to discourage--involvement by TSPM members in the democracy movement. Moreover, the TSPM tended to be strongest in China's cities. Thus, Christians associated with the TSPM tended to be better informed about what was happening politically in the country. On the other hand, as Lambert points out, most house-church believers were in the countryside and thus less well-informed about political events (p. 218). Furthermore, given that house-church Christians were already in a precarious position vis-a-vis the government given their unofficial status, they may have been wary of becoming involved in a political movement, since that could have caused them further trouble.
Nevertheless, despite their differing responses to the 1989 democratic movement, both Protestant believers in the TSPM and in the house churches would end up being adversely affected in the aftermath of the June 4 massacre. As part of a general crackdown by the Communist regime, there was a noticeable trend in the following years toward asserting government control over both official and unofficial churches. Nonetheless, some three decades on, Christianity continues to grow in China. However, just as was the case after the Tiananmen Square Massacre, Chinese Christians continue to need the prayers of their fellow believers outside of China as they are facing renewed efforts toward government control of the church under the hardline leadership of Xi Jinping.
Image of Tiananmen Square, Beijing, in 1988 from Wikimedia Commons