The phrase "easing upon" conveys a sense of gradually reducing pressure, restraint or tension. An antonym for "easing upon" would be "intensifying," which connotes a process of increasing pressure, stress, or strain on something or someone. Another antonym could be "tightening," which suggests a process of becoming more strict, severe, or rigorous. Alternatively, "clamping down" could be used as an antonym, which implies a sudden and forceful application of pressure or control. In all cases, antonyms for "easing upon" denote a process that results in more resistance, tension, or constriction, rather than relaxation or release.