The US firm was one of a eight internal portals slapped with a fine after inspections revealed apartments advertised on the site did not appear in the region's official register of tourist properties.
The site was also running advertisements for individual rooms in private apartments, something which is illegal in Catalonia.
The region's government — known as the Generalitat — is now even looking at blocking access to the site, Spain's El País newspaper reported on Monday.
In addition, Airbnb will have to immediately stop displaying listings for illegal properties.
"Barcelona should stay on the cutting edge of innovation, and we’re disappointed to see a ruling that affects diverse companies and that will hold the city back," said the company in a brief statement provided to The Local.
"Regarding our particular case, while we review this decision and consider our legal options, we will continue to provide robust information about the rules in Barcelona, and require all Airbnb hosts to follow those rules."
The decision to fine the region is the latest development in Catalonia's attempts to regulate a sector where there are thought to be as many as one million illegal beds. Local tourism operators also companies like Airbnb are taking away business from legitimate operators.
In 2013, Spain updated its rental laws, but the regulation of holiday apartments was left to the country's 17 autonomous regions.
Catalonia was among the most proactive in cracking down on the unregulated apartment sector, and some 200,000 such properties have now been legalized.
A recent report comissioned by the company into Airbnb's operations in Barcelona revealed revenue of €128 million a year. That report also suggested the company's business had generated over 4,000 jobs in the city.
The report also showed 75 percent of the people who rented out apartments via Airbnb had incomes at or below the national Spanish average.
Along with its tough stance on holiday rentals, Catalonia has also gone out on the attack against the mobile taxi app Uber.
The region recently announced it would fine drivers using Uber up to €6,000.