A crack down on illegal camping has been launched following an increase in people staying in car parks overnight.
Pembrokeshire council is staging early morning patrols and issuing fines of up to £70 to tackle the rise in so-called "wild camping".
About 20 penalty notices were issued to people caught parking illegally last weekend, the council said.
Camper vans and vehicles on lay-bys and verges are causing access problems for emergency services.
Mark Davies, a civil enforcement officer, begins his patrol at 05:00 BST and said a growing number of penalty notices were being issued, especially at weekends.
"You can see people have been having a couple of drinks, not bagging the rubbish and taking it home, just leaving it for the local authority to clear up," he said.
"It is frustrating - people think they can get away with it because they're enjoying themselves.
"If they follow the rules then everyone can enjoy it. Some people spoil it for a lot of others."
Officers are also reporting a number of camper vans and other vehicles parked on verges or in lay-bys - which can cause access problems for emergency services and put lives at risk.
They are also leading to problems such as littering and people using parts of the national park as a "public toilet".
Tegryn Jones, chief executive of the Pembrokeshire Coast National Park Authority, said the local infrastructure and fragile coastal environment could not cope with unauthorised stays.
"We set up the county to cope with day visitors - obviously when they're staying and they're cooking, then they'll fill the bins and you'll see litter all over the place.
"We've also seen instances of people emptying toilets in lay-bys, which is not pleasant and certainly doesn't add to the experience.
"The local community is dependent on tourism, it's difficult then when people don't follow the rules - it has a negative impact on the lives of other visitors and on local communities."
Wild camping, in a tent or camper van, is banned in Wales without the landowner's permission.
Marc Owen, street care and parking manager for the council, said tensions were high.
"We've had issues in car parks and on highways - some people are unfortunately leaving rubbish behind.
"We've got fantastic campsites in the county, so we're not saying don't come, we're saying please come to visit, but visit safely and pre-plan your trip.
"Car parks aren't set up for overnight camping - they're set up to be car parks."