There are several synonyms for the phrase "works against" that could be used in a variety of contexts. For instance, "opposes" is a synonym that indicates an active stance against something or someone. Another possible synonym is "hinders," which implies that something is interfering with progress or success. "Thwarts" is another word that could be used to indicate an active effort to stop or prevent something. Additionally, "counters" could be used to describe a response or action that is meant to neutralize or offset the effects of something else. Overall, there are several effective alternatives to the phrase "works against" that could help to add variety and precision to your writing.