Newsquest Sussex, which publishes Brighton's Argus newspaper, confirmed that 21 jobs will be relocated to the Indian operations of US firm, Express KCS.
The move, which would result in a cut from 31 prepress employees to the equivalent of just 10, was announced to staff last week with a four-week consultation period now under way.
The planned end date for the consultation period is 19 May.
Unite national officer Steve Sibbald told printweek.com: "If these jobs are outsourced 5,000 miles away, [Newsquest] can't promote this paper as local.
It doesn't matter if the jobs move to India, New York or Newfoundland, it simply contradicts the impression that the publisher is creating."
"We want to make the local communities aware that when these products, which are being peddled as local, it is not the case."
He suggested that outsourcing the work would also be "detrimental to the quality of the output".
A statement to staff from Ian Hunter, group production manager of Newsquest Sussex, said that the decision followed the installation of proofing and workflow software.
"Newsquest is continually looking at production efficiencies," it said. "This is particularly important given the current external challenges and pressures on our business."
"99 times out of a 100, when redundancies are hinted at, redundancies will be made," said Sibbald.