Beefeaters guarding the Tower of London face "heartbreaking" redundancies to cut costs following a drop in visitors.
The pandemic forced the closure of six sites run by Historic Royal Palaces (HRP), and "dealt a devastating blow" to its finances, bosses said.
The Tower attracted nearly three million visitors in 2018, making it the UK's most popular paid for attraction.
HRP confirmed a voluntary redundancy scheme was in place and compulsory redundancies were likely to follow.
The organisation believes it is the first time the guards have faced redundancy since the unit was formed by Henry VII in 1485.
John Barnes, HRP's chief executive, said: "Historic Royal Palaces is a self-funded charity. We depend on visitors for 80% of our income.
"We are heartbroken it has come to this.
"We have taken every possible measure to secure our financial position, but we need to do more to survive in the long term.
"We simply have no choice but to reduce our payroll costs."
The temporary closure to visitors has created a £98m shortfall this year, HRP said.
This is made up of current losses, the high maintenance costs of heating and providing electricity to large properties, and an expected slow recovery in tourism.
Last year it cost HRP £32m to run its six sites, which include Hampton Court Palace and Kensington Palace.
At least two of the 37 Yeoman Warders, nicknamed Beefeaters, who guard the Crown Jewels, have reportedly taken voluntary redundancy already.
The site reopened on 10 July but only welcomes fewer than 1,000 people each day due to new safety measures - a huge drop from the 12,000 who would visit on a normal day.
The head of the Public and Commercial Services Union, which represents many workers at HRP sites, said the decision to cut jobs "is a disgrace".
General secretary Mark Serwotka said: "Our members help guard the Crown Jewels and keep historic royal monuments and premises clean and safe.
"They should not be paying for the effects of the coronavirus pandemic."
A spokesman for the prime minister said: "We recognise the important role which the Beefeater guards play in the UK's rich cultural history.
"We are providing unprecedented financial assistance, which many heritage organisations including the Historic Royal Palaces have taken advantage of."