I would do everything to be reassigned to another task. It’s a very serious health issue for those of us who are highly sensitive. Perhaps you can get a note from your physician. You can buy protective coveralls to wear but the trick is not touching anything that has come in contact with the oil. It’s very hard to not touch your face, brush your hair out of your eyes, touch a water bottle, etc. Tecnu is a good product but it’s not a miracle cure, best to avoid exposure if you can.
Wow, I never expected to get this many responses! Thank you to everyone who responded! 
For those who asked if I could get reassigned, I don’t think it’s possible.
-Basically, people are in their own program (ex. Science, Justice, Health, etc.) and they will go with people in the same group as a “team-building” activity. They’re trying to make us “bond” before the school year starts with people in our program.
I’ve never actually had a severe allergic reaction to poison ivy so I can’t get a doctors note.
When they mentioned that we’d be doing a service day (early-July), I didn’t mind. They examples they provided us seemed harmless (ex. preparing meals, painting at local elementary schools, etc.) About two weeks ago, they confirmed the specific sites for each group and warned that “many students will be around poison ivy”. They provided no contact info for people who have questions or concerns about service day, so I’m thinking of emailing their main email address to ask about it.
@1or2Musicians There are 12 groups. Me too, I was wondering why they couldn’t find a safer activity for us if they could find one for every other group. The other 11 have relatively safe activities, like preparing lunches, planting flowers and trees, and sorting donations.
Once again though, thank you everyone for your responses! i really appreciate it!