The CDC recommends that all women with hepatitis B should be encouraged to breastfeed their newborns. Read the Full Report.
The benefits of breastfeeding outweigh any potential risk of infection. Since it is recommended that all infants be vaccinated against hepatitis B at birth, any potential risk is further reduced.
For women taking antiviral treatment, there is data from HIV literature to support the safety of lamivudine and tenofovir during breastfeeding, but please discuss with your doctor if you have concerns.