Cubans have overwhelmingly ratified a new constitution that reaffirms that socialism on the island is “irrevocable” while also legalising modest economic reforms instituted over the last decade.

But in an unprecedented display of ballot-box dissent on the Communist-ruled island, more than 700,000 people voted “no” to the new founding document.

86.85% of those who voted answered “yes” to the question, “Do you ratify the new constitution of the Republic”. 9% of voters opposed ratification and 4.15% spoiled or left ballots blank. Turnout was 84.4%

The state had campaigned hard prior to the vote, casting a “yes” vote as an act of patriotism and a vote for the Revolution. TV, radio, posters, billboards and huge banners unfurled over public buildings urged the population to get out and vote. Even the electric ticker boards on buses chugging along Havana’s main thoroughfares read “I Vote Yes” (“Yo Voto Sí”).

But the state was met with a surprisingly forceful challenge from an unofficial campaign against the new constitution.

Evangelical churches concerned that the new constitution would create a pathway towards gay marriage hung banners reading “marriage: man + woman” from church walls, while religious activists daubed posters on lamp posts – a direct challenge to the state’s monopoly on public space.

Although pastors did not explicitly call for a “no” vote, analysts say the church campaign mobilised non-religious, socially conservative sectors of the population to vote against the new constitution.

And while state media gave no airtime or column inches to critical voices, #I’mVotingNo (#YoVotoNo) hashtags were trending on Facebook.

While older citizens said they voted to support the government, a younger generation of Cubans, particularly those living in the cities, are more daring.

Cuban journalist Mónica Rivero, 29, said: “I think the new constitution is too conservative. It crystallises the status quo rather than making changes.”

In Cuba’s last referendum on a constitution in 1976, during the Cold War, 98% of ballots voted “yes”.

Voting on the island is optional though strongly encouraged by the state and nosy neighbours. Cuba does not allow international observers to monitor its elections but citizens are allowed to watch the vote count at local polling stations.

The new constitution reaffirms the Communist Party as the only legitimate political party on the island, defines access to health and education as fundamental rights, and claims that humans can only “reach full dignity” through “socialism and communism”.

But there are also big changes. The new constitution introduces presidential term limits and enshrines the right to legal representation upon arrest.

The document also gives constitutional backing to cautious pro-market reforms carried out since 2011. Private property is recognised, the rights of multinationals investing with the state are strengthened, and the market is recognised as a fact of life.

Analysts estimate that one million Cubans now work in the private sector.

Emily Morris, an economist from University College London, said the new constitution might open the path to stronger labour rights for those working in the island’s non-state sector.

“Worker exploitation is already happening in the private sector,” she said. “But recognising private enterprise could be a step forward by facilitating improved regulation of relationships between employers and employees.”