Alan Fincke has been renting out two rooms in his Cambridge, Massachusetts, home for the last three years, using the website Airbnb to do it.

He's semi-retired and uses the extra money to help pay the bills, and he's enjoyed the company.

"It's really opened up our two little rooms to the world travelers," said Fincke.

But with the popularity of Airbnb and other websites that are used to share homes, there are growing concerns. In both Cambridge and Boston, city officials are looking at new regulations.

"We have people looking at Airbnb as an investment opportunity," said Cambridge City Councilor Craig Kelley. "And they're not connected physically to that particular unit."

Kelley says Fincke is not someone officials worry about because he's renting out rooms in his own home. But they are concerned about investors buying up properties and turning them into permanent short-term rentals, which can lead to a decrease in the housing stock and an increase in rent for local residents because of the tightened demand.

"We have a lot of Airbnbs and in a market as tight as Cambridge I think it's reasonable to think that there is some negative impact on availability of market-rate long-term housing," said Kelley.

In Boston, City Councilor Sal LaMattina tells necn there are hundreds of housing units being used as what he calls virtual hotels, making it difficult for residents to find affordable homes. Landlords are turning it into a full-fledged business.

A spokesperson for Airbnb tells necn the problem is not systemic, and in Boston for example, only about 5 percent of the listings are being used for commercial purposes.

"We believe focusing on a certain and minute number of listings unfairly represents how the average and the large majority of our Massachusetts hosts use the platform -- which is typically less than 40 days per year," said Crystal Davis in a statement from the company. "The typical Boston and Cambridge family is using home sharing to pay their bills, save for retirement or reinvest in their homes. Wherever we work with lawmakers, we rely on lessons learned in cities where Airbnb is a good neighbor. In Massachusetts, we've had a number of collaborative conversations about sensible regulation, fair taxation and we will continue on that path."

The Boston City Council is planning a meeting next month to discuss new regulations. Cambridge had a meeting Wednesday night about the same issue. But new rules for Airbnb are not imminent.

"I just hope that when regulations come out, that they're not going to have a dampening effect on Airbnb hosts in the city," said Fincke.