Police investigate alleged attacks on Labour activists in Batley
Three arrests have been made - one for possession of an offensive weapon.
Labour activists in the Batley and Spen by-election have been pelted with eggs and kicked in the head while on the campaign trail, the region's mayor has said.
Newly elected West Yorkshire mayor Tracy Brabin said she was leafleting with "colleagues, volunteers, campaigners" in the Whitaker Street area of Batley on Sunday when they "were followed, verbally abused and physically assaulted by a group of young men".
Ms Brabin, who was the Labour MP for the constituency before winning the metro mayor job in May, said: "The group I was with included young people and the elderly. I witnessed them being egged, pushed and forced to the ground and kicked in the head".
West Yorkshire Police confirmed on Sunday evening that they are investigating, and Ms Brabin - who also holds the police and crime commissioner responsibility for the region - praised officers for their swift response.
But she added: "We know why tensions are rising in our streets. Those who want to sow division are not welcome in our community.
"The actions of these people do not represent the Batley and Spen I know. We are kinder than this."
Labour MP for Halifax Holly Lynch added: "There has been a series of increasingly serious and violent attacks in recent days and this is absolutely unacceptable.
"Lawless thugs are seeking to intimidate and attack those involved in the proper democratic process."
It comes after Labour leader Sir Keir Starmer condemned as "disgraceful" the abuse Labour candidate Kim Leadbeater faced while campaigning on Friday.
A total of three arrests were made - two for public order offences and a man was also arrested for possession of an offensive weapon.
Officers also assisted two people who are believed to have suffered medical episodes.