The agents downed tools last Monday and only resumed work this morning following the intervention of ZRA commissioner general Kingsley Chanda and Eastern Province PS Chanda Kasolo.
The agents want Ngulube to be removed and his predecessor who is on suspension reinstated.
Both Kasolo and Chanda warned that the agents would have their licences revoked if they continue with the strike.
Kasolo said the action by the agents amounts to economic sabotage and warned that they risk being arrested.
Some drivers who were found on both sides of the border complained over the strike action by the agents.
Chanda ordered that the all the marooned trucks should be cleared by end of business today.