Russian President Vladimir Putin wants marriage to be defined as the union of a man and woman in a revised constitution, ruling out gay marriage.
It is among several constitutional amendments proposed by Mr Putin, which are set to be put to a public vote.
Critics see the proposals as a move by Mr Putin to keep a hold on power after his presidential term ends in 2024.
The package includes a proclamation of Russians’ faith in God and a ban on giving away any Russian territory.
The territorial amendment would strengthen Russia’s hold on Crimea – a Ukrainian region it annexed in 2014 – and the Kuril Islands, disputed with Japan since World War Two, according to Vladimir Mashkov, a renowned actor-director involved in drafting the new constitution.
Mr Putin also proposed an amendment on “historical truth”, to protect “the great achievement of the people in their defence of the Fatherland”.
He has railed against what he sees as foreign attempts to diminish the enormous sacrifice made by the USSR in World War Two. The defeat of Nazi Germany cost an estimated 27 million Soviet lives.
- What Putin’s plans mean for Russia
- Do Russians care what Putin does next?
- Vladimir Putin: 20 years in 20 photos
- Vladimir Putin: Russia’s action man president
Mr Putin is in his fourth presidential term; he has been the dominant figure in Russian politics for 20 years. His presidency has been marked by a revival of Soviet-era symbols, conservative values and the influence of the Russian Orthodox Church.