“Sometimes with inquiries such as these you get to a stage where you are just not getting anywhere and we need to get vital evidence to help move things along,” a spokesman said.
“The information we are after relates to a full range of supplier issues.”
He said the letters would compel suppliers to provide evidence and other material.
The CC would not say which suppliers had been issued with the letters.
The commission has repeatedly been asked to get more pricing information from suppliers. Its Emerging Thinking document came in for criticism from the Association of Convenience Stores earlier this year for failing to get sufficient information from suppliers.

