When a new home is built, buyers expect the best. But there are a number of homes in Colorado causing the worst, according to attorney Mark Nelson.

"A pungent smell that irritates the eyes, nose, and throat," Nelson said. "It's apparent to anyone who goes into one of those basements, particularly basements that are unfinished."

Nelson said the cause is formaldehyde leaking out of floor joists (the support for floors) made by a Seattle-based company called Weyerhaeuser. The company used a formaldehyde-based resin in a formula to improve fire resistance in their product labeled as "TJI Joists with Flak Jacket Protection".

Nelson filed a lawsuit on behalf of two families who said the smell and chemical made them sick.

"At least initially, they were told, it's a new home smell. Don't worry about it," Nelson said.

The impacted homes are new. They were all built after December 1, 2016. Last month, Alyse Smith told 9News that her new Aurora home was causing her problems every time she went down to her basement.

"My eyes are already stinging and watering," Smith said in July. "They sting really bad."

Nelson said his clients not only got sick, but they are now essentially homeless.

"They've been displaced. They're living with other family members or in hotels for an indefinite period of time," Nelson said.

Another attorney Frank Azar filed a federal class action suit on Friday believing this issue could impact hundreds of people. Weyerhaeuser said in a previous statement in July that about 2,200 homes were impacted nationwide.

Wednesday afternoon, Weyerhaeuser released another statement.

"Our top priority is to take care of every homeowner and builder affected by this situation. We are working closely with builders to resolve the issue as quickly as possible, and remediation is already scheduled, in progress, or complete in more than 1,000 homes. Affected homes are in various stages of construction and most are not yet occupied. For any displaced homeowners and buyers, we are arranging and covering the cost for temporary housing until remediation is complete. We deeply regret this situation and are working diligently to do the right thing for everyone who is affected."

The company added:

“As a policy, the Company doesn't comment on pending litigation.”

Nelson said if you have home built after December 1 and experience a strong smell along with sickness, leave your home immediately. If you are unsure, he says to get it tested by a professional. He believes this is just the beginning of something big.

"A lot of people who call us don't even know about this issue and they've been in their home for months," Nelson said.