Construction workers near Ellon say it has been three weeks since cleaners tended to the toilets.
They are dualling the A90 Aberdeen to Peterhead road between Balmedie and Tipperty as part of the £745 million Aberdeen Western Peripheral Route Project.
One whistleblower claimed some colleagues had been so desperate they went into the woods, while others had driven to nearby shops and restaurants.
He told the Evening Express: “When I first started here there was a cleaner that would come twice a day.
“Now they have one cleaner for the whole thing who has been off, and it’s absolutely disgusting.
“The smell is horrendous.”
Aberdeenshire East MSP Gillian Martin has now written to Aberdeen Roads Ltd seeking further information on what action was being taken.
A Transport Scotland spokesman said the north section management team had been notified, adding: “Aberdeen Roads Limited, the project contractor, takes its responsibilities seriously.”