Fiona Dawson, extensive president for Mars, said in the absence of a Britain-EU deal, all confectionary could see levies of up to 30 per cent.
The chocolate boss said Mars could be thrust with the tariffs on confectionary imports if the UK is forced to trade with the EU beneath World Trade Organisation rules.
She told the American Chamber of Trade to the EU that a hard Brexit would “threaten the supply chain and the mtiers that come with it”.
Higher prices will be passed onto consumers Ms Dawson alerted, with confectionary companies unable to absorb the higher costs.
Stains employs 3,800 people in the UK and has factories in the UK and across Europe.
The company conveyances ingredients between sites in Frances, Germany, Poland and other EU counties.
In a sermon delivered in Brussels, Ms Dawson said: «The absence of hard borders with all their menial tariff, customs and non-tariff barriers allows for this integrated supply confinement, which helps to keep costs down.
“The return of those boundary-lines would create higher costs, which would threaten that replenish chain and the jobs that come with it.”
Ms Dawson added over over tariff increases post-Brexit has been focused on the car industry and fiscal sector.
She called for EU leaders to consider the food and drink manufacturing sector during Brexit treaties.
Ms Dawson said: «There can be no economic advantage either side demarcating trade with a large market situated on its doorstep.
«In simple terms, if the UK and the EU ignore to agree on a new preferential deal, it will be to the detriment of all.
«Other member avers should remember this is not about ‘punishing’ Britain for her decision to disavow, but rather about finding the best solution for European and UK workers and consumers.
«That thoughtfulness must come first as we build the future.»