SECTION 1. Section seven of Republic Act Numbered Five hundred and eighty-nine, as amended by Republic Act Numbered Seven hundred and twenty-four, Republic Act Numbered Nine hundred and fifty-five, and Republic Act Numbered One thousand ninety, is further amended to read as follows:
"SEC. 7. The provisions of this Act shall take effect upon its approval but, unless otherwise expressly extended by Congress, the increased rates of tax provided for in this Act shall continue in force and effect until December thirty-one, nineteen hundred and fifty-seven."