It has a sales office in Paddington Central, London, while in Cardiff it has a client services team based at Llanishen and a retail centre in Rhiwbina.
One company no longer working with Gill's is Carnival UK, which includes P&O Cruises, Cunard, Princess Cruises and Seabourn Cruises.
Carnival UK's sales and customer services director Giles Hawke said his company severed the agency relationship with Gill's earlier in the week week because of increasing concerns about its financial position.
He added that if customers had booked a Carnival cruise with Gill's their holiday was safe.
Rochelle Turner, head of research for Which? Travel, said the travel industry had been through some turbulent times over the past two years.
"Gill's is the most recent in a long list of travel companies that have suffered as a result of the economic downturn," she said.
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