Members of Flex Gym on Broncos Highway said the gym never notified them.
Richard Lachapelle told NBC 10 he lost about $450 after paying to renew a membership for him and his wife.
"(The owner) took, from what I understand, one membership at 7 p.m. Friday night, and closed the doors at 9 p.m. that night," he said.
Lachapelle wasn't alone. Gym employees found out with little warning.
"We just heard rumors from different customers and basically Friday night I got a text message from my boss saying that Flex was out of business and thanks for your time with us," said former employee Emily Trudeau. "We get paid weekly. I got that Friday morning when I left my shift for the weeks' worth of work last week. I don't know if I'll get paid."
The gym's owner lives in Connecticut, and Trudeau said she considered him almost like family because she's been going to the gym for so long and working for him.
One woman told NBC 10 that the owner recently made some donations to events.
"Unfortunately those will go unused and unaccounted for," the woman said.
Elite Fitness Center in Smithfield is trying to work with customers who were given no notice of losing their memberships.