All employees should pay for their own parking fees, especially those in government-leased space. Many lease agreement have "free spaces" built into the lease. It is free to the employee but not the government and usually the highest graded employee is the one getting the free space.
If the government has to pay for space, the only time the space should be given to an employee for free, is to give the space to employees who must have a vehicle available to perform their job. These employees save the government funds by using private vehicles instead of using GSA government leased vehicles. Because they use their own vehicle, they give up the opportunity to use public transportation or car pool. They must have their car available for government-approved travel.
All federal employees should pay for their parking, not the United States taxpayer.