Subway announced this week that eventually it will stop using azodicarbonamide — a chemical used in yoga mats and shoe rubber — as an ingredient in its bread.

But representatives for Subway, which apparently does not use the chemical in its European or Australian markets, would not say when the company would actually effect the changes.

Although Subway claims the change was already underway, the announcement coincided with an online petition asking Subway to substitute healthier ingredients. The petition, started by Vani Hari, an activist who has targeted other fast food companies over chemical ingredients, had more than 60,000 signatures by the time Subway responded.

Still, Subway's representatives refused to elaborate on the timeline.

A representative for Subway says the change was underway before the petition was launched, but did not immediately provide details on when it started or when it would be complete.

"The complete conversion to have this product out of the bread will be done soon," Subway said in a statement, without providing further details.

[image via AP]