BANGKOK (AP) — Thailand's main opposition party announced Sunday its members were resigning en masse from Parliament to protest a government they claim is illegitimate, a move sure to deepen the country's latest political crisis.

Democrat Party spokesman Chavanond Intarakomalyasut told The Associated Press his party could not work in the legislature anymore because the body is "no longer accepted by the people."

The minority Democrats are aligned with anti-government protesters who have staged the country's biggest rallies in years, vowing overthrow Prime Minister Yingluck Shinawatra's administration through mass demonstrations.

The Democrats have not won an election since 1992, and the protesters are demanding a non-elected people's council lead the country.

Yingluck's government came to power in a landslide vote in 2011, a ballot that observers said was free and fair.

Thailand has been plagued by political turmoil since Yingluck's brother Thaksin Shinawatra, a former premier, was toppled in a 2006 military coup.

At least five people have been killed and at least 289 injured since the protests began last month.

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  • Anti-government protesters gather in the compound of Government House in Bangkok, Thailand Tuesday, Dec. 3, 2013. (AP Photo/Sakchai Lalit)

  • An anti-government protester celebrates after opening the gate of the Government House in Bangkok, Thailand Tuesday, Dec. 3, 2013. (AP Photo/Wason Wanichakorn)

  • Anti-government protesters remove concrete barriers outside the Government House in Bangkok, Thailand, Tuesday, Dec 3, 2013. (AP photo/Wason Wanichakorn)

  • A Thai policeman salutes to anti-government protesters from inside the government house building, in Bangkok, Thailand, Tuesday, Dec. 3, 2013. (AP Photo /Manish Swarup)

  • Anti-government protesters cheer after pulling down concrete barriers outside the Government House in Bangkok, Thailand, Tuesday, Dec. 3, 2013. (AP photo/Wason Wanichakorn)

  • Anti-government protesters remove a barbed wire outside the Government House in Bangkok, Thailand, Tuesday, Dec 3, 2013. (AP photo/Wason Wanichakorn)

  • Anti-government protesters remove concrete barriers outside the Government House in Bangkok, Thailand, Tuesday, Dec 3, 2013. (AP photo/Wason Wanichakorn)

  • Anti-government protesters pull down a concrete slab near city police headquarters in Bangkok, Thailand, Tuesday, Dec. 3, 2013. (AP Photo /Manish Swarup)

  • An anti-Government protester raises his fist after getting into the compound of Government House in Bangkok, Thailand Tuesday, Dec. 3 2013. (AP Photo/Wason Wanichakorn)

  • A truck loaded with anti-government protesters drives into the compound of Government House in Bangkok, Thailand Tuesday, Dec. 3, 2013. (AP Photo/Wason Wanichakorn)

  • An anti-government protester hugs a Thai policewomen outside city police headquarters in Bangkok, Thailand, Tuesday, Dec. 3, 2013. (AP Photo /Manish Swarup)

  • A Thai policeman offers a rose to protesters outside city police headquarters in Bangkok, Thailand, Tuesday, Dec. 3, 2013. (AP Photo /Manish Swarup)

  • An anti-government protester gives roses to Thai policewomen outside city police headquarters in Bangkok, Thailand Tuesday, Dec. 3, 2013. (AP Photo /Manish Swarup)

  • Roses offered by anti-government protesters decorate a Thai policeman's bulletproof vest outside city police headquarters, in Bangkok, Thailand Tuesday, Dec. 3, 2013. (AP Photo /Manish Swarup)

  • Anti-government protesters wave Thai national flags and yellow flags with an emblem of the Thai king as they listen to leaders speaking at Government House in Bangkok, Thailand, Tuesday, Dec. 3, 2013. (AP Photo/Vincent Thian)

  • An anti-government protester hugs a Thai policeman as others watch them outside city police headquarters in Bangkok, Thailand , Tuesday, Dec. 3, 2013. (AP Photo /Manish Swarup)

  • Thai anti government protester celebrate after break the barricades during demonstration at the Government House in Bangkok on December 3, 2013. (PORNCHAI KITTIWONGSAKUL/AFP/Getty Images)

  • Anti-government protestors cheer as they sit on the road near the Metrpolitan police headquarters in Bangkok on December 3, 2013. (INDRANIL MUKHERJEE/AFP/Getty Images)

  • An anti-government protester takes her photograph with a Thai policeman on the road leading to the Metrpolitan police headquarters in Bangkok on December 3, 2013. (INDRANIL MUKHERJEE/AFP/Getty Images)