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Factory bosses say businesses will quit Kent entirely should port owners close down Chatham Docks.
The shock news from Peel L&P - which owns the site in Medway - was confirmed last week putting 800 jobs at risk.
KMTV reports on the closure
The company said it will close the area in 2025 because the site is not financially viable but the move has sparked angry reaction from MP Kelly Tolhurst.
But bosses have disputed the claims saying their businesses are performing well with an annual turnover of £150 million and they do not want to leave the Towns.
Phil Taylor, chief executive of ArcelorMittal Kent Wire, said: "We totally refute Peel’s line that Chatham Docks aren’t viable. Our businesses are living proof that the docks are thriving and we invite anyone who doubts that to come and see for themselves.
"We have 800 highly skilled manufacturing and port related direct employees - many of whom are local people - with more again employed through our supply chains."
Peel says it will be consulting with businesses about relocating their operations to Sheerness - a port the company also owns.
But Mr Taylor says the Sheppey port "is just not suitable for the type of vessels" needed by the businesses currently operating at Chatham Docks.
He added: "The reality is if Chatham Docks goes to the wall so do our businesses and so do the livelihoods associated with them."
It comes after 10 firms - including Arcelor Mittal - joined forces to set up an association to fight the Chatham Waters development encroaching on the port.
The Association of Chatham Docks Commercial Operators launched as managers feared the development would set a precedent for further housing at the riverside development and it expanding into the docks.
Although no formal applications for Chatham Docks have been submitted to Medway Council, those fears are a step closer to reality with Peel confirming the port will shut.
Council documents show Peel L&P put forward the land for redevelopment when the authority issued a call for sites last year.
The land was earmarked as being "suitable, available and achievable" to be considered for new housing, leisure and retail under the council's Strategic Land Availability Assessment (SLAA).
Further assessments have been carried out by planning officers who will decide whether to include the area in the first draft of the new Medway Local Plan - forming an updated development masterplan for the entire Medway area until 2037.
The draft plan is due to be published next month.
If the SLAA submission for Chatham Docks was included in the new draft Local Plan - and then approved - it would replace the current blueprint published in 2003.
That plan established a formal policy specifically relating to the port stating the council would "support the continued operation and future expansion" of Chatham Docks.
The document also states applications relating only to "general industry, storage and distribution" would be acceptable.
The council reiterated its support to protect Chatham Docks in 2012 when one of the 75 conditions applied to the Chatham Waters scheme stated developers must repair or replace the lock gates to "aid in the retention of the commercial dock" in accordance with the Medway Local Plan 2003.
Mr Taylor added Peel L&P has not yet approached companies about moving to Sheerness but questioned who would pay the expenses to relocate.
In 2012, ArcelorMittal spent £3m to remain at Chatham Docks.
"I kept the business in Chatham because Medway Council gave written undertakings that Chatham Docks was not required to meet house-building targets set by central government and existing wharf and port capacity would be safeguarded," Mr Taylor added.