A reservist could be subject to the UCMJ during inactive duty training (drill). However, cases of reservists being punished under the UCMJ for missing drills are rare to non existent. Members of the National Guard, while not subject to the UCMJ during drill, may face additional penalties from their particular state.
In normal drilling status Air and Army National Guard reservists are usually under Title 32 (National Guard), rather than Title 10 (Armed Forces) status. This leaves punishment for such offenses to the individual states. The rules for guard members missing drill and what can be done about it vary from state to state. In practice, punishments for missing a part or all of a weekend drill range from nothing, to not being paid, to having to make up the drill, and in some rare instances arrest and punishment. GI Rights Hotline Counselors can provide information regarding the rules and likely risks of punishment in different states.