Activist Srisuwan Janya has accused retailers of violating consumers' rights in ceasing to hand out single-use plastic bags while failing to offer suitable alternatives.
Mr Srisuwan said the move allowed major stores to eliminate the cost of providing plastic bags from Jan 1, and to pass the burden to their customers.
"Some operators took the opportunity to unreasonably raise the prices of alternative containers, and consumers have no choice but to buy them.
"It is the duty of stores to offer alternative free and environmentally friendly containers, instead of cashing in on their customers," he said.
He also accused the government of failing to protect consumers rights. He urged the Office of the Consumer Protection Board to step in and do its job.
The decision to stop handing out free single-use plastic shopping bags from Jan 1 is part of a campaign by the government and major retailers to help reduce the amount of plastic trash dumped into the environment.