Whenever the city rent agency shall find, after making such studies and investigations as it deems necessary for such purpose, or for processing an application supported by adequate proof filed by an interested party pursuant to regulation that the percentage of vacancies in all or any particular class of housing accommodations in the city, as such class is determined by the city rent agency, is five per centum or more, the controls imposed on rents and evictions by and pursuant to this chapter, with respect to the housing accommodations as to which such finding has been made, shall be forthwith scheduled for orderly decontrol, with due regard to preventing uncertainty, hardship and dislocation, by order of such agency; provided, however, that notwithstanding any provision of this section to the contrary, such agency shall not order the decontrol of any particular class of housing accommodations as to which it shall find that the percentage of vacancies is less than five per centum; provided, further, that no such order shall be made unless such agency shall hold a public hearing on such proposal at which interested persons are given a reasonable opportunity to be heard. Notice of such hearing shall be provided by publication thereof, on at least five days during the period of fifteen days next preceding the date of the commencement of such hearing, in the City Record and in at least two daily newspapers having general circulation in the city.