labour under a misconception BrE
labor under a misconception AmE

He told parents that we were 'all labouring under a misconception' if we thought reading was in a healthy state.

'Apparently you're labouring under a misconception, Mr Grayle.

"I discovered that we have been laboring under a misconception," he said, finally.

I think you may be laboring under a misconception.

"Apparently I've been laboring under a misconception."

In the Sachem school district, with a proposed tax increase of 12.6 percent, voters may be laboring under a misconception, the superintendent, James Ruck, said.

In December, when rumors began circulating that she would soon return to France, Prime Minister Lange said she was "laboring under a misconception."