Drivers parked on the roadside near the Storey Arms over the weekend after the visitor car parks overflowed.
But Dyfed-Powys Police said the number of parked cars led to "significant disruption and traffic issues", and it started handing out notices.
About 115 drivers were issued with tickets, set at £50 each.
The force tweeted: "If your vehicle is one of those parked on A470 Storey Arms you are in the process of receiving a parking ticket. Move your vehicle please."
Tom Martin, 30, said he was "astounded" to see rows of cars with yellow parking tickets plastered on their windshields.
"I couldn't see anything telling people not to park on the side of the road, and there were hundreds of cars there by late morning so it would've looked like a legitimate parking spot to people passing by," he said.
James Morgan wrote on Facebook: "I think people are missing the point here. The roads were impassable.
"It was bedlam there - hundreds of cars parked on grass verge for miles. It made access for emergency vehicles impossible."
Insp Matt Scrase said: "We have to ensure that emergency vehicles have access in the event of an incident.
"This was particularly important over the weekend when road conditions were poor and there was an endurance event taking place."
More than 100 drivers who parked on the A470 to visit the Brecon Beacons National Park during snow have been hit with nearly £6,000 of fines.