By default, the import utility is bound to the database with isolation level RR (repeatable read). If a large number of rows is being imported into a table, the existing lock may escalate to an exclusive lock. If another application working on the same table is holding some row locks, a deadlock will occur if the lock escalates to an exclusive lock. To avoid this, the import utility requests an exclusive lock on the table at the beginning of its operation.
Holding a lock on the table has two implications. First, if there are other applications holding a table lock, or row locks on the import target table, the import utility will wait until all of those applications commit or roll back their changes. Second, while import is running, any other application requesting locks will wait until the import operation has completed.