Other biocides are available

"Chlorine-washed chickens" has become a handy term to sum up European objections to a no-strings trade deal with the USA. Pedantic Trumpites have objected that only a minority of poultry processors in the States use chlorine or chlorine compounds (I have seen an estimate of 20%), so here for more completeness are the most cited bacteria-killers I have found in use in the food industry:

• chlorine gas
• cetylpyridinium chloride
• acidified sodium chlorite
• peracetic acid
• bromine and bromine salts
• trisodium phosphate

The European Food Standards Agency evaluated four common bactericides and concluded that they were probably safe, subject to further studies on the build-up of resistance in the various bacteria. However, as the European Consumer Organisation points out,

There are two different approaches to meat safety. The first prevails in the European Union and is known as the ‘farm to fork’ approach. It ensures hygiene and safety all along the production chain via preventive steps. These include on-farm biosecurity to prevent animal infection in the first place (e.g. use of dedicated clothes and footwear by farm workers), proper transportation conditions, hygienic slaughtering and processing practices, etc.) 

The second prevails in the United States and essentially monitors safety of the end product. It favours‘end-of-pipe’ treatments such as spraying or dipping meat carcasses with chemical cleaning solutions in abattoirs to reduce bacterial contamination.

So by accepting poultry imports on US terms we are also accepting lower farming standards, either putting our farmers at a disadvantage or necessitating scrapping EU standards which have built up over a generation. For me at least there is also the lingering suspicion that taste might be affected and, if the decontamination process is not done properly, the creation of carcinogenic compounds.