Motorists are being warned of delays around the Gladstone Road area of town as roadworks begin today (Monday).
Gladstone Road will be closed to southbound traffic from today for around four weeks while Cadent works on replacing the gas main.
An official diversion route has been set up.
Spencer councillor Gareth Eales, also the Labour Parliamentary Candidate for Northampton South, has raised concern over the works.
Cllr Eales said: "The section in between Newport Road and Raymond Road is closed to southbound traffic, so you can still drive up Gladstone Road, but not down.
"Southbound buses are being diverted into Newport Road and Countess Road, then turning left onto Spencer Bridge Road.
"I am hugely concerned about this and have formally registered my concerns with Highways, those roads are tight at the best of times, so putting diverted traffic including buses down them worries me."
Drivers are being warned that delays are likely until around November 28.