"This ruling will surprise and concern many UK businesses, and indeed public sectors employers, who had been following the law to the letter," Allie Renison, Head of EU and Trade Policy at the UK's Institute of Directors, said in a release.
"The notion that the period mobile workers spend travelling between home and their first client in the morning must count as working time goes above and beyond the protections intended by the law," Renison added.
The ECJ said that excluding such journeys from working time would mean failing to protect the health and safety of European workers.
Renison went on to say that, "the ECJ has become a red-tape machine, tormenting firms across Europe."
The ECJ, which is based in Luxembourg, ruled on a Spanish case between a security equipment company, Tyco, and its workers. Tyco's employees are provided with company vehicles, and use them to travel to and from jobs during the day. The traveling distances between the workers' homes and the jobs they are assigned vary greatly and can last up to three hours, the ECJ said.
The ramifications of the decision could be huge. "The decision has immediate application and employers have no choice but to comply," Suzanne Horne, Partner and Employment Lawyer at global law firm Paul Hastings LLP, said in a release.
Horne went on to add that, "Aside from the salary costs, there are additional questions about how this impacts an employee's entitlement to daily rest breaks and the 48 hour maximum working week, as well as other employer liabilities, such as travel expenses."
Commenting on the ruling, Andy Alderson, CEO and founder of van leasing broker Vanarama told CNBC via email that, "Our customers are mainly small employers and this additional cost is really going to hurt the growth of their business, at a time when growth should be encouraged."
Alderson added that, "No matter what profession you are in, people need to get to work regardless. It's ludicrous to suggest that journey time needs to be accounted for."