Popular Democratic Movement (PDM) leader McHenry Venaani said Jerry Ekandjo's proposed anti-gay law must pass a constitutionality test.
The amendment bill, which seeks to define the term spouse and amend the Marriage Act of 1961, will now have to pass the legality test in the National Council, he said.
Venaani was speaking in parliament on Wednesday, during a heated debate over an amendment to the civil registration and identification bill, which was tabled earlier this week.
Disagreement over the definition of "spouse" prevented members of parliament from voting on clause 1 of the bill's amendments, which was different from Ekandjo's private member's bill.
The civil registration and identification bill now defines marriage to mean a "union between a man and a woman of full age and concluded in terms of the laws governing civil marriages in Namibia", and the "union between a man and a woman of full age and concluded under any customary law of a Namibian traditional community".
The bill makes provision to exclude same-sex unions or any union concluded in Namibia, and the reference to 'spouse' excludes a person in a same-sex marriage or union.
In the marriage amendment bill tabled by Ekandjo as a private member's bill, spouse is defined as "a person being one half of a union between a genetically born man and a genetically born woman of the opposite sex of that person".
The voting of the civil registration and identification bill is at the committee stage, but had to be postponed after several MPs queried the different definitions.
Home affairs minister Albert Kawana and his deputy Daniel Kashikola anticipated that the law would be passed before the National Assembly went into recess yesterday. However, both the opposition and Swapo MPs stood firm and requested that Kawana and Kashikola explain why the bills define spouses differently.
Popular Democratic Movement lawmaker Maximalliant Katjimune said: "Can we really have different laws that speak to different definitions of the same thing?"
Swapo lawmaker Natangwe Ithete said the civil registration and identification bill must adopt the same definition of spouse as Ekandjo's latest marriage amendment bill, while information minister Peya Mushelenga also insisted on Ekandjo's definition of spouse.
"There were particular words that were used in the (marriage amendment) bill for specific purposes. To talk about a genetically born man and woman is to prevent someone from leaving this country, going through several operations, and coming back."
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Swapo lawmaker Becky Ndjoze-Ojo said the objective of amending the Marriage Act is due to "people making changes to their womanhood and manhood".
Kawana rejected the argument that the civil registration and identification bill must adopt the definitions in the marriage amendment bill because the National Assembly passed it first.
He said the amendments, including clause 1 that defines marriage, were the result of debate during the first and second readings of the bill in the National Assembly.
"It is a misrepresentation to say this one came after because it was fully motivated here by my colleagues."
Kawana also said the bill's amendments were certified by the attorney general, who serves as the chief legal adviser to the head of state and the government.
"Should a legal issue arise against the government, it will be the attorney general who will be at the forefront."
Landless People's Movement leader Bernadus Swartbooi agreed with Kawana, saying the attorney general's input on bills does not overrule parliament.
Swartbooi highlighted that even if the National Council passes Ekandjo's private member's bill, the president may ask the attorney general to review the law's legality and constitutionality.
He said the different definitions of spouse in the two bills is why the attorney general "should have been involved".
Meanwhile, Kashikola said both definitions "aim at one point, which is to prevent what we don't want".
