Thanks for the quick reply but if I use Disable, will future duplicate inserts be prevented? I think the table will allow duplicate rows.
Also, I went ahead and created it with the disable clause as suggested and tried to enable it with the novalidate option:
ALTER TABLE EMPOWER.U_SMCSHIPPING ENABLE NOVALIDATE CONSTRAINT CHASE_NUM_UNIQUE;

Got the same error msg:
ORA-02299: cannot validate (EMPOWER.CHASE_NUM_UNIQUE) - duplicate keys found

Thanks,
Robel