Unless you have a contract with your employer which guarantees you gas compensation, it is purely discretionary or voluntary for the company to provide it--that is, the law does not make a company compensate employees for gas or fuel costs. Since it's voluntary for your employer to provide this compensation, they may take it away at will--and put any conditions they want on getting it (such as driving with a topper). And if they don't pay it to  you, they may do with it as they please, including donating it.If you do have a contract requiring that you get gas compensation, then they have to honor the terms of the contract.