ambiguous

If I assign the same name to 2 columns in 2 different tables:

+--------------------------------------+
| DEPARTMENT |
+----------+----------------+----------+
| LOCATION | DESCRIPTION | DEPT_NO |
+----------+----------------+----------+
| Bedrock | Administration | 1 |
+----------+----------------+----------+

+--------------------------------+
| EMPLOYEE |
+---------+------------+---------+
| EMPL_ID | NAME_LAST | DEPT_NO |
+---------+------------+---------+
| 1 | Slate | 1 |
+---------+------------+---------+

select * from DEPARTMENT, Employee where dept_no = '1';

PG throws up:
ERROR: Column 'dept_no' is ambiguous

Is this not allowed? or is my sql understanding wrong?

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