A grant may be made or contract entered into under section
300 or
300a of this title for a family planning service project or program only upon assurances satisfactory to the Secretary that—
For purposes of this subsection, the term “low-income family” shall be defined by the Secretary in accordance with such criteria as he may prescribe so as to insure that economic status shall not be a deterrent to participation in the programs assisted under this subchapter.