Vaghela, who had earlier slammed the Gujarat unit of Congress over "lack of homework" for the assembly polls due later this year, claimed that the function is not a show of strength.
He said he only wants to share "his feelings" with the people and give a message.
The event has been named as 'Sam-Samvedna Sammelan,' a gathering of people to share their feelings.
"Since July 21 is my birthday, my supporters have decided to celebrate it and convinced me to attend the gathering. During that function, I will share my feelings with the people and also give them a message. That message will be in the interest of the people of Gujarat," he said.
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"This is not a show of strength. I just wanted to respect the feelings of my supporters, especially those from my constituency Kapadvanj," said the former Gujarat chief minister.
"See, this event is technical, as I am inviting MLAs in my capacity as the LoP. Otherwise, there can never be an invitation to attend a birthday celebration," Vaghela responded when asked if he will invite Solanki and Gehlot.
After the announcement, several key Congress leaders, such as former GPCC president Siddharth Patel, Kunvarji Bavalia and Jagdish Thakor met Vaghela at his residence.
On June 24, Vaghela had called a meeting of his supporters to decided the future course of action.