STORY: "My expectation is that most of the population will vote 'yes,'" Diaz-Canel said.
If approved, the 100-page "family code" would put Cuba at the vanguard of progressive social policy in Latin America, legalizing same-sex marriage and civil unions, allowing same-sex couples to adopt children, and promoting equal sharing of domestic rights and responsibilities between men and women.
The code, which has undergone 25 drafts, nearly 80,000 townhall-style meetings and 300,000 suggestions from the public, is expected to draw millions of Cubans to the polls. The measure requires more than 50% of votes cast on Sunday to become law.
Most prior ballot initiatives in Cuba have been overwhelmingly approved, but an economic crisis that has led to long lines for food, medicine and fuel has raised the possibility of a protest vote against the government.
Sunday's vote will be the first of its kind since mobile internet was legalized in 2018, which has let dissenting views spread more widely.
There are no independent, outside observers of Cuban elections; however, citizens may observe the count at their precincts immediately following the vote.
The government flooded TV and radio in recent weeks with spots celebrating diversity and inclusion to promote the code.