Police in Newark say shops are reporting that some of their customers aren't wearing face masks.
Face coverings are mandatory in all shops across the UK, with the government stating every member of the public must wear one in shops and supermarkets unless they are medically exempt.
The town saw a sharp rise of cases last month and an outbreak in the Bakkavor dessert factory, with Newark and Sherwood being placed on the government's coronavirus watchlist.
Bakkavor confirmed that 98 employees at the factory tested positive for Covid-19.
The number of cases has fallen recently, however, with the weekly infection rate dropping by two thirds in the seven days leading to August 24, from 38 cases to 14.
The total number of positive cases in Newark and Sherwood currently stands at 454 as of Tuesday, September 1.
But police sent out a "polite reminder" to residents in Newark to always wear a face mask while out shopping - or face a fine of up to £100.
A spokesperson for Newark Police said: "On behalf of retailers in and around the area, it has been reported that rules are not being followed in relation to wearing face masks when entering shops.
"Those who fail to do so can be fined by the police - up to £100 in England with tougher penalties for repeat offenders resulting in fines doubling each time someone is found breaching the rules."
Matt Longmire, who works at Access Models on Castle Gate, said: "There's a certain type of person who doesn't wear one.
"Yes some people are medically exempt, but others have claimed to have severe asthma but can't provide any evidence they are exempt.
"It's one of those things - and it's tricky for shops. You can't call them out on it."
A member of staff, who wished to remain anonymous, at Hills of Newark, a craft store on Barnby Gate, told Nottinghamshire Live around 20% of its customers haven't been wearing a mask properly when they enter the shop.
They said: "Generally people have been wearing them, but I'd say around two out of 10 people haven't been.
"The problem is that some people haven't been wearing them properly either - so the mask hasn't been covering their nose.
"But overall, people have been making the effort to wear them."
Sharon Porter, who is one of the managers at Jane Young, a women's clothing shop on Chain Lane, has been impressed with the amount of people wearing masks in her shop.
"Most people have been absolutely fine," she said.
"When it first started, on the very first day, people always put on a mask if we asked them to. We have a lovely little set up where we ask people to sanitise their hands when they arrive."
A member of staff at Ann et Vin, an independent wine shop in Castle Gate, said: "We have face masks in the shop that we can provide to anyone who doesn't have one.
"We just say 'would you mind putting a face mask on' and everyone does. I think I have only given three out since June 16."
