The Karen Border Guard Force (BGF) in Myanmar's Myawaddy province has closed 23 border ports along the Moei River in retaliation for curbs on oil transportation by Thai authorities.
However, the Thai-Myanmar Friendship Bridge remained open.
Gen Maung Chit Htoo, leader of the Karen BGF, yesterday ordered the shutdown of the 23 ports under its control on Myanmar's banks, which stretch from Mae Sot to Tha Song Yang district in Tak province.
The Karen BGF has a similar military structure to the Myanmar Army. Although the battalion is commanded by an ethnic armed group, the Myanmar Army has total control of the BGF's activities and both forces work together during military operations.
According to a security source, the ports were closed after more than 40 petrol trucks due to deliver oil to Myawaddy were stopped by Thai police in Mae Sot district two weeks ago because each truck appeared to exceed the 25-tonne weight limit.
Each truck weighed between 35-40 tonnes.
Oil operators asked police if the oil could be unloaded into pipelines across the Moei River to Myawaddy, but Thai police refused, and insisted the oil could only be transported via the Friendship Bridge.
The situation led to an oil shortage in Myawaddy.
Thai authorities will hold a meeting to discuss the situation, the source said.
The ports' closure affects river freight transport as cargo can only be transported over the bridge.
Col Sophon Nanthasuwan, chief of the 4th Infantry Regiment Taskforce in Mae Sot, said a meeting between state agencies and oil traders will be held in Tak's Special Economic Zone Development Office.
Meanwhile, the Myanmar government has announced that travellers crossing into the country at Tha Khi Lek from Mae Sai in Thailand will be drug-tested at random.
If the drug test is positive, offenders will be sentenced to five years in prison. Those caught in possession of illegal drugs will be sentenced to 10 years in prison. If offenders are convicted of both matters, they will be sentenced to 15 years behind bars in total. Offenders will not have their sentences commuted, or be able to pay their way out, he said.
If the tourists test positive, officials will no longer investigate the matter further to see whether the result was caused by an illicit substance, he said.
Pakaimas Vierra, chairman of the Thai-Myanmar Cultural and Economic Co-operation Association in Chiang Rai, said tourism could suffer as a result of Myanmar's new drug testing measures.
The Mae Sai-Tha Khi Lek border pass is a popular tourist attraction. During long holidays around 15-20,000 people travel across the border each day.
Myanmar's decision to impose the harsh new regulations comes after many of its citizens were detained on drug charges by Thai authorities, with many saying the cash they were carrying was impounded for inspection, Ms Pakaimas said.
Two influential figures from Shan State were recently apprehended in Thailand.
Thai officials said they will monitor any drug tests by Myanmar.