What will break the log chain is setting the database to the SIMPLE recovery mode, which is what a lot of people do when shrinking either type of file. I'll also say that it's generally a very bad idea to shrink either type of file unless there has been some extraordinary accidental growth the cause of which has been clearly identified and repaired prior to the shrink. If you can afford the disk space, you might just want to leave the gobs of freespace alone. The exception to that rule is if you know that you'll be restoring the databases to smaller servers that might not have such amounts of freespace and that also includes any Disaster Recovery machines.