The Catalan tourism sector suffered a drop in activity during the first two weeks of October "of around 15 percent" from the same period last year, Jose Luis Zoreda, vice president of the Exceltur trade association, told a news conference.
Hotel and transportation reservations through the end of the year are down by around 20 percent over the same time last year, he added.
If the drop is confirmed this would represent a loss in business of nearly 1.2 billion euros ($1.4 billion) for the Catalan tourism sector.
Exceltur -- which groups Spain's major hotel chains, travel agents, tour operators and airlines -- based the figures on a survey of its members in Catalonia.
The impact on the tourism sector appears to be stronger than that of the jihadist attacks in August in Barcelona and the nearby seaside resort of Cambrils that killed 16 people and which caused a drop in the sector's turnover of around five percent, according to the group.
Tourism sector companies have also "seriously put the brakes on all investments until the end of 2017," Zoreda said.
"If the scenario of volatility and confrontations worsens in the coming months" the drop in tourism activity could reach up to 30 percent, he added.
The drop in activity would affect employment as the sector employs around 405,000 people in Catalonia, he added.
The impact of the slowdown in tourism, which represents around 12 percent of Catalonia's economic output, could be the "same or more significant" than the flight of company headquarters out of the region in recent days, Zoreda said.
Catalonia, with its capital Barcelona and Costa Brava beaches, is the Spanish region that most attracts foreign visitors.
More than 18 million visitors went in 2016, or a quarter of all foreigners who came to Spain.
Britain, Germany and several other countries issued travel warnings to their citizens who planned to visit Catalonia ahead of the banned independence vote in Catalonia.
Shocking videos filmed on the day of the vote beemed around the world showed police dragging voters from polling stations by their hair, throwing people down stairs and attacking Catalan firefighters protecting polling stations.
Since the referendum noisy street protests have been held in Barcelona by both advocates and opponents of independence, which have added to concerns about visiting the region.