Eurostar says it is "fighting for survival" with demand down 95%, and claims state relief for airports put it at a "direct disadvantage" to airline competitors.
Its plea for greater financial support comes after chancellor Rishi Sunak earlier this week announced the government would cover up to £8 million in business rates at each of England’s major airports.
Prior to the pandemic, Eurostar operated up to 50 services a day; this is now down to just a single London-Paris train and one Brussels-London service.
In a statement, Eurostar said: "The new scheme of rates relief for airports puts Eurostar at a direct disadvantage against its airline competitors.
"Eurostar has been left fighting for its survival against a 95% drop in demand, while aviation has received over £1.8 billion in support through loans, tax deferrals and financing.
"We would ask this scheme to be extended to include international rail services, and more generally for the government to incorporate high-speed rail in its support for the travel sector, and in doing so, help protect the green gateway to Europe."
Unions too have called for government intervention. Mick Cash, general secretary of the RMT union, said ministers must "step in immediately" and provide Eurostar with the financial support it needs to continue fulfilling its "important international infrastructure role" and ensure it continues to directly and indirectly support thousands of jobs.
"It is wholly wrong that Eurostar, an eco-friendly service that is a beacon for the future of our railways, is being denied the kind of financial support being offered to the airports," said Cash.
"The current inaction leaves the service hanging by a thread, and all we are asking for is the support needed to maintain viability and stability as we move out of this phase of lockdown and look forward to the future."
Manuel Cortes, general secretary of the TSSA union, which represents Eurostar train manager and customer service advisors, added ministers "must not sit on their hands" with Eurostar "looking at a cliff edge".
“Our members have been at the forefront of this pandemic, making sure trains run smoothly and safely for passengers," he said. "What they need now is assurances their jobs are safe and Eurostar has a strong future.
“We have already seen the extended closure of Ashford and Ebbsfleet stations, and for months our union has been warning that help was needed.
“Eurostar simply can’t be allowed to fail. A proper support deal will see this vital green strategic link between Britain and our European neighbours through Covid crisis and put on a firm footing for the future.”