May said it was "absolutely ridiculous" that Cadbury promoted its chocolate egg hunts without reference to the Christian festival.
May said it was "absolutely ridiculous" that the National Trust, which runs parks and stately homes across Britain, had allowed sponsor Cadbury to promote its chocolate egg hunts at their sites without reference to the Christian festival.
"I'm not just a vicar's daughter -- I'm a member of the National Trust as well. I think the stance they have taken is absolutely ridiculous," the prime minister told Britain's ITV News while on a trip to Jordan.
"Easter's very important. It's important to me. It's a very important festival for the Christian faith for millions across the world."
Her comments came after the Archbishop of York, John Sentamu, told The Daily Telegraph newspaper that the move was "tantamount to spitting on the grave" of chocolate maker Cadbury's founder, John Cadbury, a Quaker.
A Church of England spokesman also told the paper that advertising materials for the egg hunts were "airbrushing faith from Easter".
The National Trust owns or manages large swathes of the British countryside, from coastlines to historic buildings and parks -- and each year it holds family-friendly egg hunts over the Easter long weekend.
This year's campaign is called the "Cadbury Egg Hunt", although the chocolate maker pointed out that other marketing materials urge children to "Enjoy Easter Fun".
A Cadbury spokeswoman said: "It is simply not true to claim that we have removed the word 'Easter' from our marketing and communication materials."
The National Trust, for its part, said: "It's nonsense to suggest the National Trust is downplaying the significance of Easter. Nothing could be further from the truth.
"We host a huge programme of events, activities and walks to bring families together to celebrate this very special time of year."
Meanwhile Hampton Court Palace, one of several royal palaces run by a separate charity, is holding a "Lindt Gold Bunny Hunt" as part of its "Easter family fun".