Rashtriya Lok Dal on Friday withdrew support to the one-year-old Mayawati-led Bahujan Samaj Party-Bharatiya Janata Party government.
Party chief Ajit Singh handed over a letter to Governor Vishnu Kant Shastri at 12.45 pm to that effect.
Singh arrived in Lucknow from Bhopal, where he had kept his 14 MLAs, in the morning and straightaway went to the governor's house.
Singh decided to pull out of the Mayawati government after he was forced to give up the Union agriculture portfolio one day before the May 24 Cabinet reshuffle effected by Prime Minister Atal Bihari Vajpayee.
On Thursday, Singh met Samajwadi Party chief Mulayam Singh Yadav and Congress president Sonia Gandhi on the possibility of putting up an alternative coalition to the BSP-BJP one.
Singh told rediff.com that he was confident of bringing down the Mayawati government.
"With the entire opposition having risen up in arms, I can see that the days of the Mayawati government are numbered," Singh said.
"We have urged the governor to dismiss the Mayawati government since it was our mainly on the support of the BJP and RLD that he had invited Mayawati to form a government," he said . "Now, that we have pulled out of the coalition, her government automatically stands reduced to a minority."
Shastri, however, maintained, "I will have the issue examined by constitutional experts, before which it would not be appropriate for me to make any comment."
The last time, Mayawati faced a no-trust move in the state assembly, she had romped home with the support of 222 MLAs in an elected house of 402 (excluding one nominated member). Even after the withdrawal of 14 RLD members, she still commands a strength of 208.