May Day is traditionally held on a Monday, but will be put back to Friday, 8 May in 2020 to accommodate the 75th anniversary of VE Day.
But Simon Aherne and Anna Cousins, from Cardiff, say the lack of notice has left their plans in tatters as most guests will be unable to attend.
Do pass this on - lots of people may make the 'usual' holiday plans for May Day next year but it's NOT Monday!