Even before the Martial Law days, Jopson was active in the student movement, becoming president of the National Union of Students of the Philippines. One of the most memorable anecdotes of the time involved Jopson and other student leaders going to Malacañang for a dialogue with Marcos in 1970, and insisting the president sign a written pledge not to run for a third term of office. Marcos retorted that he would not agree to a demand from a mere "grocer's son."