[pnh102]

You should study up on this stuff first.

According to the linked article the USPS union contracts state that no workers can be laid off for economic reasons.

[muawiyah]

That depends on how you interpret "economic reasons". The law also says you can't shut down a post office for not making a profit.

What you can do is transfer work to another area and lay off the surplus people. You can wait on lightning to set fire to the post office and close it anyway. You can offer early retirement and simply dispose of the incumbent's previous job. You can also HOLD A RIF ~ a reduction in force.

It's just a matter of will.