Braden Phillips

Special for USA TODAY

BARCELONA — Shopkeeper Esther Royo wasn’t planning to vote in Catalonia’s controversial independence referendum Sunday until the Spanish government threatened to block it as illegal.

Now Royo, 32, is determined to cast her ballot, though she won't say if she favors breaking away from Spain. “I’m going to vote because they want to take it away,” she said. “I have the moral right.”

The central government in Madrid has seized millions of ballots, detained 14 senior officials organizing the vote, shut down election websites and deployed thousands of police to bar access to voting stations.

The Interior Ministry has sent an additional 10,000 riot police and other officers to Barcelona, the capital of Catalonia, one of 17 semi-autonomous regions.

“This referendum now cannot happen. It was never legal,” said Spanish Prime Minister Mariano Rajoy.

In defiance, Carles Puigdemont, president of Catalonia, vowed to push ahead with Sunday's vote and declare independence from Spain within 48 hours if the pro-independence vote prevails.

"As president, I have the right to call a referendum based on a law that the Catalan parliament has approved. The vote will go ahead," Puigdemont, 54, said in a phone interview with USA TODAY.

Three years ago, around 80% of the electorate backed independence but only 42% of Catalonia’s 5.4 million voters turned out, according to government statistics.

Today, Catalans are split over seceding. A recent poll by digital publication El Español put support for independence as high as 50%. But Spain’s response has galvanized Catalans to defy the government. A GAPS poll released this week predicted 600,000 more voters will turn out Sunday than had planned two weeks ago — which amounts to 63% of the electorate.

Islamic State terror attacks six weeks ago that killed 15 people in Barcelona and nearby Cambrils has raised concerns around the vote and the possibility of a violent confrontation with police. “I’m not afraid personally, but my husband and I will vote one at a time rather than take the kids with us,” said Elena Farro, 37, a pharmacist.

The potential for heightened tensions in Catalonia is the greatest since dictator Francisco Franco’s long rule ended with his death in 1975. A split electorate could lead to an inconclusive result that would trigger a standoff between separatist leaders in Barcelona and a central government determined to keep Catalonia as part of Spain.

The wealthy region, where 7.5 million of Spain's 46 million people live, accounts for approximately one-fifth of the country's economy.

With its own language and culture, Catalonia’s tug-of-war with Madrid goes back to the Middle Ages, when it was an independent region. In 1714, Spain absorbed Catalonia. Many still have vivid memories of how Franco sought to suppress Catalan culture, even outlawing the Catalan language.

After Franco, Catalonia achieved pseudo-autonomy within Spain. Some said they would prefer to expand self-rule.

More:Catalonia independence vote: Why it's happening, and why it matters to U.S.

More:Leader of Catalonia separatist vote vows to press ahead for independence amid tensions

“I will vote for independence, but I believe more in a federal state within Spain. I think independence will fail,” said Jose Deulofeo, 90, who lived through the 1936-39 Spanish Civil War between a democratic government and Franco's victorious fascist forces. “But we have to push for independence to force the federal solution.”

Farro’s colleague at the pharmacy, Cristina Mondet, 27, disagrees and will vote against independence.

“Puigdemont is ignoring the law. A democracy needs to follow laws if it is going to function,” she said. “What if I say I don’t want to pay taxes? They (pro-independence supporters) are playing games with democracy.”

Contributing: Kim Hjelmgaard