HAVERHILL, Mass. -- Four Haverhill firefighters face suspension after calling in sick and then getting caught on tape doing strenuous activities such as moving furniture, shoveling and plowing snow and shopping.

NewsCenter 5s Gail Huff reported Tuesday that the city says it's costing them a lot of money.

"We think it's apparent that if you say you're sick you're supposed to be sick," Haverhill Mayor James Fiorentini said.

The mayor paid $13,000 to hire a private eye to follow "sick" firefighters with a video camera.

The firefighter's union calls it unfair labor practice, and it's appealing the five-day suspensions.

"They feel violated. Their kids and spouses were videotaped, and they feel violated," said Paul Weinburgh, of the Haverhill Firefighters Union.

The mayor said firefighters call in sick nearly four times more often than other city workers -- costing hundreds of thousands of dollars in overtime.

He claims to have used private investigators in the past to follow teachers, policemen and others, but a former Haverhill policeman questions that.

Two weeks ago, contract negotiations between the city and firefighters union broke down.

"There's nothing that says we have to be sitting at home in bed when we're on sick leave," Weinburgh said.