Manly Fast Ferry has warned commuters that all services from Manly to Circular Quay have been suspended due to strike action.
According to a spokesperson, members of the Construction, Forestry, Maritime, Mining and Energy Union (CFMEU) are blocking access to the boats.
"Manly Fast Ferry is urging passengers attempting to board ferry services between Manly and Circular Quay to be patient," a statement says.
"Members of the CFMMEU have illegally boarded ferries and are forcibly preventing passengers from boarding.
"Management want to ensure the safety of all its passengers, staff and those protesting."
Fast ferry workers had planned to strike between 8am and 10am this morning over a pay dispute, claiming that all skippers have been employed on a casual basis since the current seven-year contract was signed in 2015.
The NRMA, who took ownership of the operator in 2017, have denied that skippers are paid less than the award rate.