How to optimize a query...

I originally had this query with an OR clause instead of the UNION,
which made it amazingly impossibly slow, with the UNION it's far faster
however it's still very slow,(10,000+ rows in both stables), is there a
way to speed this up? I have BTREE indexes on all concerned fields of
the tables, but it doesn't seem to use any of them...

I have another query that joins the result of this with 5 other
tables, unfortunately that one takes like 10 minutes... Any suggestions
on optimizations would be very appreciated.

ftc=> explain
ftc-> select po_id,ticket_pk
ftc-> from tickets,po
ftc-> where po_id=material_po
ftc-> union
ftc-> select po_id,ticket_pk
ftc-> from tickets,po
ftc-> where po_id=trucking_po
ftc-> ;
NOTICE: QUERY PLAN:

Unique (cost=4744.05 size=0 width=0)
-> Sort (cost=4744.05 size=0 width=0)
-> Append (cost=4744.05 size=0 width=0)
-> Hash Join (cost=2372.03 size=11659303 width=12)
-> Seq Scan on tickets (cost=849.03 size=19213
width=8)
-> Hash (cost=0.00 size=0 width=0)
-> Seq Scan on po (cost=528.98 size=10848
width=4)
-> Hash Join (cost=2372.03 size=13838477 width=12)
-> Seq Scan on tickets (cost=849.03 size=19213
width=8)
-> Hash (cost=0.00 size=0 width=0)
-> Seq Scan on po (cost=528.98 size=10848
width=4)

EXPLAIN