A man and a woman have been arrested after more than 30 people claimed to have had money taken out of accounts when their credit cards were skimmed.
Norfolk Police said an investigation was centred on a Jet petrol station in Great Yarmouth where they have removed equipment and documents.
They said people paying for fuel at the petrol station had been targeted.
A 43-year-old man and a 40-year-old woman from the Great Yarmouth area were arrested and are being questioned.
A spokesman from Norfolk Police said they believed people paying for fuel with a card were being watched as they put in their PIN numbers.
He said it was vital that people kept their PIN number private.
A spokeswoman for ConocoPhillips, which supplies fuel to the petrol station, said it took any allegation regarding credit card fraud very seriously.
She said the company was working with owner and operator Murphy Oil Corporation to investigate the card-skimming allegations.
The said it had strict policies and worked closely with police and operators to safeguard customers' security.