Britain's Maritime and Coastguard Agency said that some fo the crew had been onboard for more than 12 months.
Five cruised ships from the same company have been detained by British authorities over concerns for crew welfare.
Britain's Maritime and Coastguard Agency (MCA) revealed that it inspected six ships from Global Cruise Lines Limited on Friday and that five have been detained.
"Surveyors found a number of expired and invalid Seafarers Employment Agreements, late payments of wages and crews who had been on board for over 12 months," the MCA said in a statement.
Four of the ships are flagged with the Bahamas and one with Portugal.
A spokesman for Cruise and Maritime Voyages (CMV), which operate the ships, said that the company "cooperated fully" with investigators.
"The MCA has identified some issues relating to expired crew contracts and crew being onboard in excess of 12 months. Both issues occurred as a result of the enforced lockdown period and the Covid-19 travel restrictions for some countries. They also identified recent temporary delays in the payment of wages which were due within the last week and have already been corrected by CMV," he added.
"The health, safety and welfare of all their passengers and crew is CMV’s top priority. CMV, as have many other cruise lines, has faced an unprecedented emerging humanitarian issue as many crew members became stranded on cruise ships as borders closed as a result of the global outbreak of the Covid-19 pandemic. CMV has worked hard to repatriate as many crew members as possible and has been unable to repatriate all crew members due to the travel restrictions," he also said.
Some 600 of the six ships' crew are Indians, according to Kshitij Thakur, a lawmaker in the state of Maharashtra.
Thakur demanded in a letter sent to the Indian government that the sailors, who "have been stuck in foreign waters for almost 90 days", be repatriated as soon as possible.
The All Indian Seafarers Union added in its own letter to the New Delhi government that many of the sailors onboard one of the vessels, the Astoria, had gone on hunger strike and staged a peaceful protest in a plea for help.
The International Maritime Organisation (IMO) described seafarers earlier this week as both "the unsung heroes of the pandemic" and the "collateral victims of the crisis".
More than 80 per cent of the world's trade by volume, including vital food, medical goods, raw material and manufacturer goods, are transported around the world by sea in vessels staffed by a global workforce.
These seafarers, who spend several weeks or months at sea, are often flown between their home countries and ports of departure and arrival. But travel restrictions imposed to curb the spread of the COVID-19 virus, have left tens of thousands of them stranded on ships, or unable to join ships, the IMO said.
"Repeated extensions of their contracts have now reached a level where this cannot continue without serious consequences for the health of seafarers and consequentially, for the safety of the ships they operate," the IMO warned.
It estimated that starting from mid-June as many as 300,000 seafarers each month will require international flights to enable crew changeovers and that about half of them will need to be repatriated home by aircraft while the other half join ships.
An additional 70,000 cruise ship staff are also currently awaiting repatriation, it said.