Workers hired to load coal to run the steam engines of Darjeeling’s toy trains have been on strike since Tuesday as they have not been paid salaries for August, The Times of India reported on Thursday.

As a result, the British-built steam locomotives, which run between Darjeeling and Ghoom, have not been operating for the past three days. The Darjeeling Himalayan Railway has been forced to refund tourists who had booked their rides months in advance.

The United Nations Educational, Scientific and Cultural Organization, or UNESCO, granted the service World Heritage Site status in 1999 to ensure that the steam engine legacy continues.

The workers who haul between 600 kg to 800 kg of coal onto each train for an average of three trips a day have alleged that their contractor has not paid them their wages for August. They have threatened to continue their strike till their dues are cleared.

Darjeeling Himalayan Railway Director NK Narzary said the strike has tainted the legacy of the world heritage site. “If the situation does not improve, we will have no option but to blacklist the contractor and appoint a new one,” Narzary told the Hindustan Times. The director claimed the contractor, Pramod Chettri, had not submitted the bills on time. Chettri could not be contacted.

Narzary said he has initiated a dialogue with the labourers to convince them to resume work. While the railways also runs a diesel-locomotive, tourists opt for the experience of the British-era train.

The Darjeeling Himalayan Railway encountered major losses in 2017 during a 104-day agitation for a separate state of Gorkhaland. Two stations at Ghayabari and Sonada were set on fire during the protest.