Under the Employees' Provident Funds and Miscellaneous Provisions Act, 1952, the Act applies to every establishment which is a factory engaged in any industry specified in Schedule I and in which how many persons are employed? 

Section 1(3) of the Employees' Provident Funds and Miscellaneous Provisions Act, 1952 provides that the Act applies to every establishment which is a factory engaged in any industry specified in Schedule I and in which 20 or more persons are employed. The Central Government may also apply the Act to any establishment employing fewer than 20 persons by notification. Once the Act becomes applicable to an establishment, it continues to apply even if the number of employees falls below 20 at a later stage. The Act was enacted to provide for the institution of provident funds, pension funds, and deposit-linked insurance funds for employees in factories and other establishments, ensuring social security and post-retirement benefits.