def labor_supply_shock(t, states, param, t_start_lockdown, t_end_lockdown, l_s):
    """
    A function returning the labor reduction due to lockdown measures.

    Parameters
    ----------
    t : pd.timestamp
        current date
    param: np.array
        initialised value of epsilon_S
    states : dict
        Dictionary containing all states of the economic model
    t_start_lockdown : pd.timestamp
        start of economic lockdown
    t_end_lockdown : pd.timestamp
        end of economic lockdown
    l_s : np.array
        number of unactive workers under lockdown measures (obtained from survey 25-04-2020)
   
    Returns
    -------
    epsilon_S : np.array
        reduction in labor force
        
    """
    if t < t_start_lockdown:
        return param
    elif ((t >= t_start_lockdown) & (t < t_end_lockdown)):
        return l_s
    else:
        return param