No Pay when I had vacation & sick leave

In the last two weeks I had to take two days off. One was for car trouble, the other was sick leave. I had a balance on the books for both. I was asked for documentation on both which I suppllied. The manager and a young supervisor took it upon themselves to not pay me. Is this legal?
What avenue should i take. I work for The US Postal Service.

[Bricks41]

Clarify, what do you mean you had a "balance on the books for both." If you worked on both days, but had to leave after a few hours for the above mentioned reasons, they are obligated to pay you for ALL hours worked. If you intended to use vacation/pto or other hours to supplement the rest of the hours AND they fit the criteria for the useage, they owe you for those hours.

In the case of hours worked but withheld, call the Department of Labor, Wage & Hour Division.