Thailand police detained four people in the country's western Ratchaburi province on Sunday for opposing a military-backed draft charter and campaigning against it. This is the latest arrest by the authorities in the lead-up to a referendum, which is scheduled on Aug. 7.

Since the military seized power in May 2014, this referendum will be the first time when Thailand will go to the polls. The ruling government has said that the referendum will pave the way for an election next year.

Critics, including the major political parties, said that the Constitution will preserve a political role for the military and weaken civilian governments, which, in a way, will affect the turmoil that has hit Thai politics over the last decade.

The police said that the four people, including a reporter from Thai online publication Prachatai, Taweesak Kerdpoka, were detained after copies of booklets providing information on the Constitution were found in their cars.

The group of campaigners had apparently violated a law that carries a 10-year jail term for campaigning in connection with the referendum.

"They violated the Referendum Act," said Police Captain Poom Klaklaew, an investigator in the case.

This move by the junta, right before the referendum, is being looked upon as a "hardline stance on any opposition to its plans" by the other groups.

"Police found a few copies of the booklet in his bag," Kornkritch Somjittranukit, who works with Taweesak at Prachatai, told Reuters. He also said, "He told them it was material for his news report, but they arrested him anyway."

A junta spokesman, Colonel Winthai Suvaree, said that this decision of arrest was a police matter.

"The police probably didn't know who was who when they detained the group," Winthai said. "They weren't out to target the journalist."