It appears that allowing anyone to use Starbucks' bathrooms even if they haven't bought anything could be affecting the number of people who visit the cafes.

The coffee chain adjusted its policy in May 2018 in an effort to allow all customers who come in 'to feel welcome'.

The shift occurred after the arrest of two black men at a Starbucks in Philadelphia who were waiting for a friend. It became a major source of embarrassment for the company.

But it now appears that people are being put off from even stepping foot inside Starbucks as a result of the change in policy.

Since May 2018 Starbucks lets anyone use the restroom — even if they haven't bought anything but research shows fewer people may be visiting the chain

Since opening its bathroom doors to the public, there has been a 6.8% drop in store attendance per month relative to other coffee shops nearby, according to the findings of a joint study from the University of Texas at Dallas and Boston College.

'When you throw open the policy to let people come in and just use the bathrooms and the tables, maybe people come in and find the bathrooms are dirty, and the tables are crowded, and so they don't buy the coffee as well,' David Solomon, Assistant Professor at Boston College Carroll School of Management, told Yahoo Finance.

'The results in our study highlight the difficulty companies can have when trying to engage in different forms of socially responsible behavior,' Solomon explained.

The study used location data relating to 10,752 Starbucks stores between January 2017 to October 2018.

Study shows an almost 7 per cent reduction in visitors compared to other cafes but Starbucks disputes data saying customer attendance has 'exceeded expectations'

The coffee chain said it wants all customers who come in 'to feel welcome'

The data was then complied by SafeGraph which specializes in analyzing smartphone location data and algorithms.

'Our team was very interested in what the economic consequences would be of an open bathroom policy as an example of providing a public good. While the hope is always that providing public goods will be rewarded by the market with increased sales and new potential customers, this isn't necessarily the case,' Solomon noted of the study.

Starbucks calls its approach to its bathrooms a 'Third Place Policy,' meaning anyone can use the coffee shop's facilities without having to make a purchase.

The company has said the research is flawed and that sales have gone up along with attendance.

'Customers are visiting Starbucks at record numbers,' a spokesperson said in a statement.

'Rather than tracking cell phone data without user knowledge, we see real customers in our stores and the connections they make with our partners (employees) every day across more than 31,000 stores.'

Robinson (left) and Nelson (right) were waiting for a potential business partner when the store's manager called police and they were arrested

The 2018 Starbucks arrests in Philadelphia were a major embarrassment for the company which had long projected itself as socially conscious company and promoted its stores as a place for people to gather outside of their homes and offices.

The company had maintained a 'loose policy' on bathroom access, though decisions were ultimately left up to store managers on whether someone could use them.

At the Philadelphia store where the two men were arrested April 12, it was policy to ask people who hadn't bought anything to leave.

The two black men arrested for sitting at a Philadelphia Starbucks without ordering anything ended up settling with the city for a symbolic $1 each and a promise from officials to set up a $200,000 program for young entrepreneurs. Rashon Nelson, left, and Donte Robinson, right

The men, Rashon Nelson and Donte Robinson, who were asked to leave after one was denied access to the bathroom were arrested by police minutes after they sat down to await a business meeting they had scheduled.

The incident was captured by people using cellphones and went viral, leading to protests.

Nelson and Robinson settled with Starbucks for an undisclosed sum and an offer of a free college education.

Separately, they reached a deal with Philadelphia for a symbolic $1 each and a promise from city officials to set up a $200,000 program for young entrepreneurs.

The company then closed more than 8,000 of its U.S. stores for an entire afternoon of racial-bias training for its employees.