The 65-year-old newspaper, founded initially to support anti-fascists in the Spanish Civil War, is currently run as a collective. However, a recent board meeting saw members agree that the weekly needs a major cash injection in order to secure its future, and one way of doing this could be by selling.
A relaunch in April 2001, which saw the newspaper change its format from a newspaper to a magazine, similar in style to The Spectator or New Statesman, failed to give it a boost in sales.
A spokesman for Tribune said: "We're still trading fine, but after our relaunch we haven't had the expected increase in sales." He added that the possibility of a sale had been brought up at a board meeting, but that no further action had been taken.
Tribune, which has been highly critical of Tony Blair's New Labour government, has a circulation below 9,000, with its eight staff reported to take salaries of around £15,000 a year.
According to The Observer newspaper, Tribune editor Mark Seddon has confirmed it is now looking for a proprietor. "We have had to take this extraordinary step because we are simply unable to market what many of us think is a much-improved paper."
Earlier this year, Tribune faced the threat of closure after Sir Ken Jackson, joint general secretary of the union Amicus, said he was suing the title for libel. However, the case was later dropped.
Contributors to the magazine over the past 65 years have included Aneurin Bevan; George Orwell, who was once the paper's literary editor; the former Labour leader Michael Foot, who was editor; Arthur Koestler; and the late Barbara Castle.
In an editorial to celebrate the newspaper's 65th anniversary, Seddon said: "Our editorial freedom is cherished because it makes Tribune beholden to no one."
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