What's wrong with this syntax?

SELECT id_1 FROM table1 WHERE state_code IN ('AZ','DE')
UNION
SELECT id_1 FROM table1 WHERE zip_code IN ('12345','54321');

Above SQL statement running fine.
Now I added

SELECT id_2 FROM table2 WHERE id_1 IN (
SELECT id_1 FROM table1 WHERE state_code IN ('AZ','DE')
UNION
SELECT id_1 FROM table1 WHERE zip_code IN ('12345','54321')
);

Now I got parse error at or near "union"
Please tell me what's wrong with the 2nd SQL statement.
Thank you!

--Raymond