The Hindu Marriage Act has the following provisions:-
Sec 3 of HMA
(f) (i) "sapinda relationship" with reference to any person extends as far as the third generation (inclusive) in the line of ascent through the mother, and the fifth (inclusive) in the line of ascent through the father, the line being traced upwards in each case from the person concerned, who is to be counted as the first generation;
(ii) Two persons are said to be "sapindas" of each other if one is a lineal ascendant of the other within the limits of sapinda relationship, or if they have a common lineal ascendant who is within the limits of sapinda relationship with reference to each of them;
(g) "degrees of prohibited relationship"-two persons are said to be within the "degrees of prohibited relationship"
(i) If one is a lineal ascendant of the other; or
(ii) If one was the wife or husband of a lineal ascendant or descendant of the other ; or
(iii) If one was the wife of the brother or of the father's or mother's brother or of the grandfather's or grandmother's brother of the other; or
(iv) if the two are brother and sister, uncle and niece, aunt and nephew, or children of brother and sister or of two brothers or of two sisters ;
Explanation.-For the purposes of clauses (f) and (g), relationship includes-
(i) relationship by half or uterine blood as well as by full blood;
(ii) illegitimate blood relationship as well as legitimate; (iii) relationship by adoption as well as by blood ; and all terms of relationship in those clauses shall be construed accordingly.
(iv) The parties are not within the degrees of prohibited relationship unless the custom or usage governing each of them permits of a marriage between the two;
Sec 5 (v) of HMA - The parties are not sapindas of each other, unless the custom or usage governing each of them permits of a marriage between the two.
Sec 11 of HMA; NULLITY OF MARRIAGE; Void marriages. Any marriage solemnized after the commencement of this Act shall be null and void and may, on a petition presented by either party thereto against the other party, be so declared by a decree of nullity if it contravenes any one of the conditions specified in clause (v) of section 5.
Sec 18 of HMA. Punishment for contravention of certain other conditions for a Hindu marriage. Every person who procures a marriage of himself or herself to be solemnized under this Act in contravention of the conditions specified in clause(v) of section 5 shall be punishable- (b) In the case of a contravention of the condition specified in or clause (v) of section 5, with simple imprisonment which may extend to one month, or with fine which may extend to one thousand rupees, or with both.
The Special Marriage Act, also has the similar provisions.
Under the above provisions, where lies the demand of change/amendment of The Hindu Marriage Act by KHAP MAHA PANCHYAT.