The memo was sent to all editorial staff by Northern & Shell, the newspaper's parent company, earlier this week.
"We appreciate the fine work you do to make the Daily Express a superb read," the memo, written by brand manager Enda Joy, begins.
"However, in line with our goal of achieving a more highbrow tone in order to attract new types of readers, it is best that we eschew any April Fool's Day stories in print, online or via our digital channels," it continues.
The memo also says that the brand is considering adding a beard, glasses and smartphone to its crusader logo - which according to Northern & Shell's website "symbolises our commitment to free speech and the newspaper’s crusade for values" and first appeared in 1933 - to give him a more "intellectual, modern" appearance.
One reporter for the paper, Claire Lee-Falls, told PRWeek: "This is all very well in principle, but how am I supposed to work out which of the press releases PRs send me are actually jokes and which are serious?"
She went on to say it was hoped the policy of no joke stories would be lifted at noon.
Editor's note: At noon on 1 April 2016, it came to PRWeek's attention that the memo in question was a figment of the writer's imagination. PRWeek would like to apologise to any readers fooled.