Hotel workers on Skye have complained of being underpaid, denied holidays and given substandard accommodation as the island experiences a lucrative tourism boom.

Trade union officials say they have been contacted by hotel staff who report being dismissed from their jobs for complaining about low wages, poor food and dismal accommodation.

The Citizens Advice Bureau for Skye and Lochalsh, which advises local people on welfare, housing and employment rights, said it gets hundreds of complaints each year from seasonal workers about low pay, overwork and lack of contracts.

Local hoteliers reject claims there is a significant problem on Skye, but the Scottish Trades Union Congress (STUC), the trade union umbrella group, believes seasonal workers are at greater risk of exploitation as hotels and restaurants struggle to cope with record levels of demand from visitors.

The STUC, which has investigated specific cases on the island as part of its “Better than Zero” campaign on workers’ rights, says the grievances of seasonal workers are being hidden in the debate over chronic overcrowding at Skye’s famous beauty spots and whether its hotels and B&Bs are now full.

Dave Moxham, the STUC’s deputy general secretary, said these cases suggested the controversy over exploitation in the gig economy and zero-hours contracts affected hospitality and tourism, too.

A significant number of seasonal workers are outsiders, including Australians, Latvians, Poles, Germans and lowland Scots, whose accommodation is tied to their jobs, the STUC said.

“Underneath the celebrated tourist trends something isn’t right,” Moxham said. “There is no use waiting for hotel owners to change exploitative conditions in the interests of profit or goodwill. Local and seasonal workers now need to fight them by coming together and asserting their rights.”

One hotel worker told the Guardian he was summarily dismissed after challenging a hotelier when his wages did not include 100 hours of overtime worked over a four-week period. “The day I got paid I queried it and said I was going to seek legal advice, and they kicked me off the premises and told me I had 15 minutes to pack my bags,” he said.

The island has become one of the most sought-after destinations for overseas visitors, particularly Americans, drawn there by heavy promotion by Scottish tourism and government enterprise agencies, and by popular TV epics such as Outlander, car adverts and pop videos.

The latest Office for National Statistics figures, released on Friday, showed that overall visitor numbers to Scotland jumped by 16.9% last year, to 3.2 million people, while their spending surged by 23%, to £2.3bn.

The unprecedented boom has led to single-track roads, laybys and small carparks at the most popular tourist sites, such as the Old Man of Storr and the fairy pools in Glen Brittle, being overwhelmed by coaches, camper vans and cars.

Tourists at Kilt Rock on the Isle of Skye, where visitor numbers rose nearly 17% last year amid a tourism boom. Photograph: Arterra/UIG via Getty Images

The island’s hotels and B&Bs are booked solidly throughout the summer, while the number of AirBnB properties registered on Skye has increased tenfold in three years, from 54 in 2015 to more than 550 this year.

Skye and Lochalsh CAB, which covers other famous destinations such as the scenic coastal villages of Plockton and Applecross on the mainland, had 485 cases in 2016-17 involving low pay and long hours, lack of contracts, unfair dismissal and either a lack of holidays or being refused holiday pay.

Morag Hannah, the CAB’s manager, said a large majority of those cases and of more than 200 additional cases over the past six months involved seasonal workers in the area’s hotels and restaurants.

“A lot of employees are scared to rock the boat – especially if it’s seasonal work – by discussing their rights with their employers, in case they’re treated less favourably or lose their shifts,” Hannah said. “There are some really good employers in the area, but we tend to hear about the not-so-good employers.”

Shirley Spear, the chairwoman of Skye Connect, an influential lobbying group set up by local businesses to help manage the island’s tourism economy, questioned why Skye was being singled out by the STUC.

Spear, owner of The Three Chimneys restaurant said fewer hotels and restaurants were employing seasonal staff, but added that irregular and long hours were part of the job.

“I can’t possibly comment on behalf of the economy of Skye, unless you want to talk about the tourism industry across the whole of the UK,” she said. “We go out of our way to make sure our employees are well looked after and have good accommodation.”

• This article was amended on 24 July 2018. An earlier version said The Three Chimneys restaurant had two Michelin stars. It had two stars in the 2015 Michelin Guide.

