Thousands of workers at consumer goods maker Unilever Plc/NV are to stage a series of strikes in an escalation of a dispute over plans to axe their final salary pension scheme, unions said on Saturday.

Last month, union members staged a one-day stoppage, the first strike in Britain in the group's 81-year history, and a rare walkout over pensions at a UK blue-chip company.

Unilever makes top brands such as Persil, PG Tips and Flora.

Leaders of three unions, Unite, GMB and Usdaw, Saturday decided to call strikes for up to 12 days starting on January 17 after nine-months of failed talks.

Unilever need to get the message that profitable companies will not be allowed to walk away from their savings commitments to their loyal workforce, Allan Black, national officer of the GMB, said in a statement.

Unilever said it remained deeply concerned by the disproportionate action the trade unions are taking, and that it was not clear how the dispute ... will be resolved.

The Anglo-Dutch group, which employs around 7,000 workers at 12 plants in Britain, is looking to move all 5,000 members promised final salary pensions to a career average scheme by July 2012.

The Unite union said this would see the retirement income of thousands of staff slashed by between 20 and 40 percent.

The company abandoned final salary pensions for new joiners in 2008 and 2,000 workers are already on the less generous scheme. The Unilever UK pension scheme has a deficit of about 680 million pounds.

This was a tough but necessary choice which reflects the realities of rising life expectancy and increased market volatility, a company spokeswoman said in a statement.

We believe the provision of final salary pensions is a broken model which is no longer appropriate for Unilever.

The three unions have about 2,350 members working at Unilever and say the company has not held talks over the dispute since October.

Union members plan to stage a demonstration outside Unilever's offices in London Tuesday.

(Reporting by Avril Ormsby)