Kenya and Uganda have banned the use of thin plastic bags in an effort to curb environmental damage.
Some Rwandan traders have defied the plastic bag ban
Ugandan Finance Minister Ezra Suruma banned the importation and use of the thinnest bags and imposed a 120% tax on thicker ones in his new budget.
The Kenyan finance minister imposed similar restrictions in his budget, following Rwanda and Tanzania.
The BBC's Juliet Njeri in Nairobi says discarded plastic bags are often seen by the roadside in residential areas.
She also says that there is a problem with bags blocking drains in the city.
Tanzania set the pace for the East African Community in 2006, when Vice-President Ali Mohamed Shein announced a total ban on plastic bags and ordered a switch to recyclable materials or biodegradable alternatives.
"These measures are expected to encourage the industry players to devise environmentally friendlier and hopefully recyclable bags," Kenyan Finance Minister Amos Kimunya announced in the capital, Nairobi.
The Ugandan minister said the ban was being introduced because of "serious environmental concerns and difficulties in the disposal of plastic bags and plastic containers."
The ban will take effect in Kenya at the stroke of midnight on Thursday 14 June.
In Uganda, Mr Suruma said the ban would come into effect on 1 July but gave traders until 30 September this year to sell off products already in stock.
Rwanda, which was admitted into the East African Community this year, banned the importation and use of plastics less than 100 microns thick in 2005.