By Joseph Akwiri

Mombasa (Reuters) - Kenyan truckers blocked the only highway from the port city of Mombasa to the capital Nairobi on Wednesday, threatening to choke the main trade artery to east Africa unless officials reverted to the old way of weighing cargo.

The east African nation is the world's largest exporter of black tea and blockage of the road to the port could disrupt shipments. Around 95 percent of all cargo arriving through Mombasa is ferried to its final destination by road, with trucks the main mode of transport.

The port, which is the main trade gateway to east Africa, also handles imports such as fuel for Uganda, Burundi, Rwanda, South Sudan and eastern Democratic Republic of Congo.

Earlier this year the Kenya Transporters Association (KTA), whose 400 members have around 50,000 trucks, struck a deal with the government over a law which limits weight loads on vehicles depending on the axle.

However, around 300 truck drivers, defying their union, used their trucks, logs and stones to block the busy highway.

"They have blocked the highway at Mariakani weigh bridge, and vowed not to open the road until the government reverts to the old system of weighing by gross weight instead of weighing the trucks per axle," KTA chief executive Jane Njeru told Reuters in Mombasa.

Njeru said KTA was already coming under pressure from businesses in Uganda to resolve the issue as they fear shortages.

However, the truck drivers, many of whom begun the strike on Tuesday, said they will not budge.

"Government must either intervene, or come and push away these trucks from the road using their bare hands because we will not remove them," said truck driver Samuel Mutiso, who was carrying medical equipment to Uganda.

Kenyan officials could not be reached for comment.

"The (officials at the weigh bridge) know the rules they are imposing on us are impossible to comply with, and so they are sure we will bribe them to pass through. This is enough," added Mutiso, as his fellow truckers waved twigs and chanted demands to be allowed to pass through the weigh bridge without being weighed.

(Writing By Drazen Jorgic; editing by James Jukwey)