Lawyers are reportedly warning that there is no automatic right to paid leave on the 29 April bank holiday.
The chances of workers getting time off work for the royal wedding will depend on their contract or employers’ goodwill.
The TUC has called on employers to honour the bank holiday - but accepted that it was not included in some workers’ leave entitlement.
The government said it hoped UK employees would get the day off.
Lawyers say it depends on the precise wording of an employment contract.
If a contract states staff are entitled to 28 days holiday per year - the legal minimum under the working time directive - there is no obligation to give staff extra time off for the royal wedding.
However, if a contract states employees are entitled to bank holidays, then 29 April should be a day off.
Although many employers do not have bank holidays noted in staff contracts, they have decided to allow paid leave.
TUC general secretary, Brendan Barber, said: “While most people are likely to get paid leave on 29 April as a result of their employer’s goodwill, a significant minority of tight-fisted companies have decided to ignore the national mood and insist on keeping staff chained to their desks while everyone else is enjoying the bank holiday.
“Not offering paid leave or overtime will rebound on employers as they risk demoralising their workforce and damaging their reputation among their customers.”
Businesses that have refused paid leave for workers have tended to argue that the extra day off would bring significant and unaffordable costs.
The TUC wants a legal entitlement for at least a day off in lieu for special bank holidays in time for the Queen’s diamond jubilee celebrations in 2012.