More than 6,000 people have been caught on charges of illegal entry since May, said the Immigration Bureau.
The office announced on Tuesday that 6,421 people had been arrested on illegal entry charges nationwide since May 1, when the country's borders were mostly shut to stem the spread of Covid-19.
It has been reported many slipped across the border to avoid the 14-day mandatory quarantine, raising the fear of imported infections which could trigger local transmission of the virus.
The bureau's announcement followed the disclosure by the immigration office in Chon Buri of the arrest of three Thai men involved in illegally importing and exporting workers through natural border channels in tambon Thep Nimit in Pong Nam Ron district of Chanthaburi.
No details were given as to when the men were arrested.
The suspects allegedly admitted to police they had been paid 2,500 baht each to send workers over the border to Cambodia.
People wanting to take up employment in Thailand paid them 3,000 baht each to be transported through the border.
Police were expanding their investigation in a bid to catch the mastermind of the gang.
The three men were charged with importing and exporting workers without permission.
Bureau commissioner Sompong Chingduang said labour gangs had operated as a network picking up workers and finding them transportation. This arrangement is for both the people entering the country illegally in search of work and those heading out to Cambodia to find work.