The decision was in violation of the Independent Broadcasting Authority Act (IBAA) because it was not equitable or consistent, said MP James Selfe.
SABC spokesperson Kaizer Kganyago was not immediately available for comment.
In a statement, Selfe said the act stated that a broadcaster was required to "treat all political parties equitably" and that "each broadcasting service should be consistent in its treatment of contesting parties and of conflicting views".
"The act contains these requirements because, to bias coverage in one direction or the other, would be to favour one political party over another and unduly influence the ability of each South African citizen to discern the choices available to them."
Selfe said the decision by the SABC promoted the views of the ANC and gave prominence to one agenda over others.
"A two-hour live crossing is incomparable with a hard news story on a bulletin.
"In doing so, it is to promote one choice before South Africans over another which is both contrary to the SABC’s mandate and undemocratic.
"Now, more than ever, the vote of every citizen can make a profound difference on 18 May," he said.