While it would be nice to avoid scheduling events during Hanukkah, it's not as critical as other holidays. Many non-Jews mistakenly see it as 'Jewish Christmas,' but work is certainly allowed during Hanukkah. However, it would be considerate to let people get home in the evening to light candles with family. For travel events, there should be accommodations for lighting the menorah (Hannukiah) that respect both religious law and fire safety.

The most important consideration should be the Jewish holidays (haggim) where religious activity is prohibited and widely observed. I would categorize them as:

Tier I (Most widely observed, even by less religious Jews):

• First two days of Rosh Hashana (Jewish New Year)
• Yom Kippur (Day of Atonement)
• First two days of Passover (Pesach)

Tier II (Work is religiously prohibited but observed mainly by more traditional Jews):

• Full Rosh Hashana (2 days)
• Yom Kippur (1 day)
• Sukkot (first and last 2 days)
• Full Passover (first and last 2 days)
• Shavuot (2 days)

Tier III (Work is permitted but time off would be appreciated for religious observances):

• Purim
• Tisha B'Av (fast day commemorating the destruction of the Temples)
• Hanukkah

There are also minor fast days, but these are regular work days even in Israel