The Samajwadi Party accused the Uttar Pradesh police of using force against its workers who were protesting against the alleged extortion by the ruling Bahujan Samaj Party (BSP) ahead of Chief Minister Mayawati's birthday on Thursday.
Over 1,000 Samajwadi Party activists were detained across the state by 3 pm, party officials said in Lucknow.
Led by senior Samajwadi Party leader Shivpal Singh Yadav, activists clashed with police in this Uttar Pradesh capital as they marched towards Mayawati's residence to hold demonstrations, they said.
Over 100 Samajwadi Party activists were hurt when police resorted to baton charge in Qaiserbagh locality in Lucknow, they added.
However, Superintendent of Police (West) Paresh Pandey said: "We only used mild force to disperse the protesters."
Ram Gopal Yadav, national general secretary of the Samajwadi Party, told reporters in New Delhi: "The police cane-charged hundreds of our partymen who were protesting peacefully and a large number of our people, including a couple of MPs and legislators, have received grievous injuries."
While Mayawati' birthday every year is celebrated as "arthik sahayog divas" (monetray help day) when her party workers collect funds for BSP, the opposition has alleged that many leaders were extorting money for the occasion and blamed an engineer's murder last month, allegedly by a BSP legislator, on the fund-raising drive.
In her speech earlier in the day, Mayawati said that her party had collected double the funds received last year "thanks to the opposition campaign".
But Yadav said: "It was due to the fear after PWD engineer MK Gupta's murder that government officials and people gave large amounts of money to save their lives."
The Samajwadi Party's acting Uttar Pradesh president Shivpal Singh Yadav said in Lucknow: "We were begging on the streets in order to collect money to donate to Mayawati when the police brutally assaulted us."
The Samajwadi Party, the state's main opposition, carried out a series of protests and demonstrations in various districts, including Gorakhpur, Allahabad, Varanasi, Saharanpur, Pratapgarh as a part of its "Thu-Thu Diwas" (condemnation day) programme.
Activists of the Bharatiya Janata Party (BJP) were also cane-charged by police as they marched to Mayawati's residence.
The Congress party also held demonstrations in Lucknow, demanding Mayawati's resignation for her party's alleged role in the killing of the engineer.