Use of antibiotics on livestock farms in the USA is now more than double the level used here in the UK.
The revelation was made by the food and farming body, Sustain, which analysed data from the US Food and Drug Administration.
The data shows total sales of medically important antibiotics for use in animals in the USA increased by 26% in the five years up to 2015.
That is twice as high per animal as it is in the UK, where Defra has recorded a 27% drop in antibiotics use on livestock farms over the past two years.
Sustain said that the Defra figures showed on-farm antibiotics use had fallen to their lowest level since records began.
The rapid decline means targets to reduce antibiotics use have been beaten two years early.
And now, Sustain is warning against flooding the British market with antibiotic-packed chicken from the US.
In a report by website Food Ingredients First, Sustain said US farmers and meat processors routinely used antibiotics, chlorine rinses and irradiation treatments on meat.
Sustain chief executive Kath Dalmeny raised concern that food produced with these standards would be sold in the UK once Brexit deals were negotiated.
“Mass-produced American chicken may seem cheap, but it comes at a gigantic cost to our health, animals and workers,” Ms Dalmeny told the website.
“British food and farming industries have started to take action on the critically important issue of overuse of antibiotics in farming. We simply cannot afford to let our trade negotiators sweep such progress aside by flooding our market with cut-price US chicken raised with routine antibiotics use,” she added.