State laws vary (of course), but apparently so.
State laws may be more restrictive, but the FLSA seems to indicate that you can dock unless it would bring the employee under minimum wage.
Cash first has only been SOP around here for 5 or 10 years. Ever since pumps started taking credit/debit cards it’s a pain to go inside and wait for all the cigarette, beer, and lottery ticket buyers to hand them cash, then go out and pump gas, and go back in again and wait in line AGAIN for change. If I have to pay cash for some reason I just give them $20, pump my $20, and leave. Even though it costs more like $45 to fill up.
There’s 2 ways the system can work. Option one is to put a $1 charge on the customer’s card to make sure it’s valid, then charge the actual amount pumped once they hang up the pump. The other option is to put a $50 or $100 charge on the card, then put the actual charge on when the pump is hung up. In both cases the holding charge drops of in a few days, but the later option can be bad if some’s card is at or near it’s limit. It also means you have to swipe the card a 2nd time if you need more gas than the hold is for.
I never made customers wait in line to get their change back, but didn’t let people cut in line to buy gas. In any even tobacco, lottery, and overpriced junk food was way more important for our sales than gas. I started a Pit thread a few years ago that rapidly turned into a trainwreck about this.
Really? As it happens, there’s a conflict in the central African nation of Bangui right now, which has led to the looting of supplies from hospitals, making it difficult for citizens of that country to receive medical aid. Good to know you’re on top of that. I’m sure you’ll straighten it out in no time.
Psst, Miller, allow me to translate:
“When I see a part of the world that mildly inconveniences me, I interpret that inconvenience as injustice, and I act like a petulant asshole to people who are doing their job as a way of exacting revenge on their bosses, who never even find out about me.”
Bangui is SOL.
Those poor people. 
Just imagine the sad sacks who operate the prepay gas stations in Bangui.
I don’t know. He’s never done it, though, because once people are told the policy, they are never willing to do it, even for their friends.
Why don’t you tell us because your strategy makes everyone hate you.
His post = “I r dat stupid.”
That’s how my Marathon (in Lake County cause taxes SUCK in Cook County) and Mobil (Cook County but they generally match Lake County prices within a dime) work - they take out a dollar immediately, and the rest is usually posted to my account the next day. The Speedway by me does it all at the same time - if I pump $20 in gas, by the time I get home, the $20 is out of my account.
Now the Shell in Lake County I went to a year ago? They took a $75 hold out at the pump where I tried to pay but the pump reader malfunctioned. So I went inside to pay for $20 in gas. ANOTHER $75 hold - on top of the $20 they took out for the gas I prepaid for. All I had left in my account for the week was around $200 at the time - so I was out $150 bucks for most of the week until it got returned. You charge me $150 bucks, plus the $20 in gas I prepaid for, and then don’t give me my money back for a week? Seriously I will never get gas at Shell again. Never.
I had one place in Indiana (I think) put a $300 hold on my card. I have a Ford Fiesta, I’d have to be pulling a freakin’ trailer to need that much gas.
I first saw this about 10 years ago and bitched like the OP did. Now it is far more common than not.
Sheetz has the best idea. You get a discount card that is linked to your driver’s license. You insert the card first and can then pump (and save 3 cents per gallon). Then you can walk inside, buy snacks, drinks, etc. and then pay for your gas. If you run off, your license is on file.
ETA: This reminds me of when I was a kid. Gas was slightly over $1 per gallon. I pumped gas and read the gallons display instead of the price. I walked in, paid $5 and left. A half an hour later, the owner calls my Dad and tells him that I cheated them out of 63 cents. My Dad asked if I could just pay the next time I was in or if the sheriff needed to come and arrest me. 
Is there anyway to see the hold that is being put on your card? I have remeber seeing such a thing on my statements.
Neither do I. My cards put a $1.00 hold on the card, and in the next couple of days I see the actual amount charged.
It’ll show up as a pending charge if you check current activity in online banking. Since it never actually posts it never appears on the statements. You could also try calling you CC company after you buy gas and ask the agent; it’ll show up on their screens.