Tens of thousands of Germans protested on Saturday against Germany's biggest austerity drive since World War Two, adding to pressure on Chancellor Angela Merkel's increasingly unpopular coalition.

Merkel's cabinet on Monday unveiled plans for 80 billion euros ($96.30 billion) in budget cuts and taxes over the next four years, but faces a challenge convincing parliament, unions and voters to accept the savings package.

Organisers said between 15,000 and 20,000 people demonstrated in Berlin, in one of the biggest protests against government reform in recent years. Police estimated that up to 10,000 people took part in protests in Stuttgart.

The crisis is called capitalism, Employment, human rights, secure future for everyone and Pensions should be enough to live on, protesters' banners read.

Merkel's government proposed saving 30 billion euros over the next four years in welfare, mainly from unemployment benefits, and slashing thousands of federal government jobs. The proposals have prompted criticism both from the opposition and from within Merkel's own ranks.

A new poll by Infratest dimap showed that 79 percent of Germans thought the savings package was not socially balanced and 93 percent thought measures were not enough to meet the government's savings goal.

Saar state premier Peter Mueller, a member of Merkel's conservatives, criticized the savings package for weighing disproportionately heavily on the poor.

If you have to tighten your belt, then the biggest belts shouldn't be immune, he told German magazine Wirtschaftswoche.

Mueller said the introduction of a luxury tax on goods such as yachts, expensive cars and champagne would be a contribution to more tax justice and acceptance of savings measures.

INCREASINGLY UNPOPULAR

Merkel, however, rejected accusations the package was unfair and told German paper Bild am Sonntag people knew that we have to save and reduce the deficit.

Her government aims to bring the structural deficit of Europe's biggest economy within EU limits by 2013, but wants to avoid raising taxes after vowing to do exactly the opposite when she took power in October last year.

Merkel argued that businesses and the civil service were also contributing to budget consolidation.

The government wants to raise an extra 2.3 billion euros per year by taxing the profits of nuclear power station operators and introducing an environmental tax on domestic air travel. In addition, a financial transaction tax is expected to raise 2 billion euros a year from 2012.

Merkel's image has taken a beating in recent months amid coalition infighting and accusations she mismanaged the euro zone crisis by delaying aid for Greece.

Now she must convince parliament and German unions to back the cuts. Her coalition lost its majority in the Bundesrat upper house after a regional election setback last month, making her task all the more difficult.

(Reporting by Sarah Marsh and Klaus-Peter Senger; Editing by Louise Ireland)