Fifa has rejected a plea from the England football team that they be allowed to wear poppies on their shirts when they play Spain on Saturday.
The Football Association had hoped football's governing body would relax the rules and allow players to commemorate Remembrance Day.
But in a letter delivered to the FA on Tuesday Fifa said allowing the request would jeopardise the neutrality of football.
"We regret to inform you that accepting such initiatives would open the door to similar initiatives from all over the world, jeopardising the neutrality of football," it said.
"Therefore, we confirm herewith that the suggested embroidery on the match shirt cannot be authorised.
"There are a variety of options where The FA can continue supporting the cause of Remembrance. One of them already was approved by FIFA, the Period of Silence."
Conservative MP Tracey Crouch, a qualified football coach (no relation to footballer Peter Crouch), said the FA should ignore the ruling.
"I think the FA/England should just ignore Fifa and wear poppies on their shirts. Let us remember...and take whatever punishment for doing so," she said on Twitter.
By way of compromise Fifa have said the teams may observe a minutes silence before the game.