From the link above:

"Approximately 70% of Vietnam was Buddhist, however the under the rule of the French and Diem there was significant favoritism shown to Christian followers, particularly Catholics. Vietnamese were encouraged to convert in order to get jobs or avoid harassment from government officials. A well known Vietnamese proverb of the time was "Turn Catholic and have rice to eat." Oppressive laws were passed against non-Christian religious practices. Monks were sent into exile and those that attempted to practice their Buddhism in spite of laws against it were harassed and even killed. In 1963 American backed Vietnamese forces opened fire on South Vietnamese demonstrators that were demonstrating for religious freedom. Nine people were killed".