The company said the job losses, which cover more than 10% of the workforce at Port Talbot, were needed to reduce costs because of lower demand for steel in Europe.
The jobs will go at Tata's strip products business, which produces sheets of steel used to make products such as tin cans, cars, roofing and fridges.
A spokesman for Tata said the company could not rule out compulsory redundancies because it needs to cut jobs while keeping hold of workers with specific skills.
The company, part of the Indian conglomerate Tata, has started a consultation process that will last at least 45 days with its employees at the site, which employs almost 4,000 workers.
Tata Steel has made a series of big job cuts in response to a fall in demand and prices for steel in Europe. It slashed almost 600 jobs in November 2012 at Port Talbot as part of a programme of 900 redundancies in the UK. It cut about 1,500 jobs in Scunthorpe and 100 in Corby the year before.
In a statement, Karl-Ulrich Köhler, Tata Steel's European chief executive, said the company had invested more than £250m in the strip products business over the last two years but that steel demand and prices would stay under pressure for several years.
"Our business rates in the UK are much higher than other EU countries and our UK energy costs will remain uncompetitive until new mitigation measures come into effect. These proposed changes then are vital if we are to build a competitive future for our strip products business in the UK."
Unions warned that the cuts should not be allowed to threaten safety at the plant and called on the government to support the steel industry.
Roy Rickhuss, who chairs the UK trade unions' steel committee, said: "We recognise the company has been dealing with a long-term downturn in European steel markets for more than five years. However we have also expressed our own concerns about possible undermanning within strip products and in Port Talbot in particular.
"This news also demonstrates that despite the government's trumpeting of economic recovery, the steel sector remains under real pressure. This sector, vital for so much of British manufacturing, must be an area of real focus for the UK's industrial policy."
Rickhuss's committee is made up of the Unite, Community and GMB unions.
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