Motorbike taxi riders and religious marshals have clashed in the northern Nigerian state of Kano over a ban that stops women travelling on the bikes.
Women say there is no public transport alternative
In accordance with Sharia law, men and women are not allowed to travel together on public transport.
Women have ignored the ban, being implemented this week, saying there are not enough transport alternatives.
Six people were wounded in the incident as a woman was told to get off a taxi motorbike on Tuesday afternoon.
The BBC's Ado Sale Kankiya in the city of Kano says some 9,000 religious marshals are on the streets to implement the ban passed earlier this year.
Despite the officials and publicity leading up to the implementation of the law, many women are still riding on the bikes, he says.
About 500 three-wheeled motorbike taxis and 100 women's-only buses have been introduced, but women say this is not sufficient.
Our correspondent says officials are not arresting or fining offenders, just warning them about the new law.
But after one taxi rider was told to drop a woman on Tuesday afternoon, more than 50 other motorbike taxi riders began fighting with religious marshals.
In Zamfara State, taxi riders have been lashed when found carrying female passengers.
For and against
Kano is one of several Muslim majority states that adopted Sharia law five years ago.
The move initially heightened tensions between Muslims and Christians and led to clashes which left thousands dead.
Human rights groups have condemned abuses sanctioned under the law including amputations and flogging, and say it discriminates against women.
Sharia law appears to have retained popular support in the north.
But there is significant opposition to the law, especially among the Christian minority.
While officially it does not apply to them, many say that in practice they are forced to comply.