KINSHASA, June 13 -- Security forces fired tear gas to break up a crowd outside the Democratic Republic of Congo's parliament on Friday, injuring the veteran opposition leader Martin Fayulu, as the country's fractured opposition united around a single charge: that President Felix Tshisekedi is engineering the legal machinery to keep himself in power past the limit his own constitution declares untouchable.

The protesters had gathered against a bill, passed by the National Assembly this week, to organize national referendums, legislation the opposition reads as the first stone in the path to a constitutional revision, Arab News reported, citing the Associated Press. The demonstration turned violent, and video circulated of Fayulu, the run...