Dharam Singh Saini earlier with the BSP, had joined the BJP in 2016.
The Yogi Adityanath government in Uttar Pradesh on Thursday lost a third minister and backward caste leader, Dharam Singh Saini, who had earlier hotly denied that he was quitting the BJP.
This is the eighth exit from the BJP in three days, with a crucial election less than a month away. They are all tipped to join Akhilesh Yadav's Samajwadi Party.
Just 24 hours ago, Dharam Singh Saini, a four-time MLA from Nakud in Saharanpur and a key OBC (Other Backward Class) leader, had rubbished reports of leaving the BJP.
He had also slammed Swami Prasad Maurya, the first to quit and set the tone for a series of exits.
"My name was wrongly given in Swami Prasad Maurya's list that is floating around. I had no idea. I am and will be in the BJP. I am not leaving the party," Mr Saini had said in a video he released to refute the reports.
But later, he returned his government home and security, tell-tale signs that he was on his way out.
Sources say Yogi Adityanath had also dialled Mr Saini to persuade him to stay.
But his resignation followed a similar pattern to that of six others, with Akhilesh Yadav playing his role by sharing a photo with the latest defector and "welcoming him". Like always, Mr Yadav used the hashtag Mela Hobe - a tweaked version of the Trinamool Congress's wildly successful catchphrase "Khela Hobey (game on)".
Earlier in the day, another backward caste leader, Mukesh Verma, quit the BJP and posted his resignation on Twitter.
Akhilesh Yadav has shared photos of his meeting with most of the eight leaders who have quit the BJP this week. The near identical resignation letters, posted on Twitter, indicate planning and strategy.
For Akhilesh Yadav, the BJP's main rival in the February-March election, the explosion of OBC leaders is a big boost.
Mr Saini, earlier with Mayawati's Bahujan Samaj Party (BSP), had joined the BJP in 2016 along with Swami Prasad Maurya and several other leaders who are moving from the BJP to the Samajwadi Party.
In the 2017 UP election, the BJP's strategy was to win over the non-Yadav OBC castes, given that Akhilesh Yadav's most loyal voters are seen to be Yadavs and Muslims.
This time round, the Samajwadi leader's gameplan is to pull in the non-Yadav OBC leaders.
"Not a single day passes when a BJP leader does not leave the party. Take UP, for example, 13 MLAs are leaving BJP to join another party. I have come to know that four BJP MLAs are leaving it today itself," Nationalist Congress Party (NCP) chief Sharad Pawar said on the defections.