A decision by the Crown Prosecution Service not to bring a prosecution after swastikas were left outside Paula Sherriff's office has been branded "disgraceful" by the Labour MP.
The Dewsbury MP said foil swastikas were left at her constituency office on three occasions last summer.
The CPS said the suspect would not be prosecuted because the test for a criminal offence had not been met.
The suspect received a harassment warning instead.
"There has been a huge increase in far-right abuse since the death of Jo [Cox, in 2016]," 43-year-old Ms Sherriff said.
She said three swastikas were left at her office in July and August, and she has had many death threats and other forms of abuse, and fears for her life.
Ms Sherriff, whose constituency neighbours Batley and Spen, where Ms Cox was killed, said the CPS ruled out a prosecution because the suspect "did not fit any charges", which she found "absolutely disgraceful".
In September, local newspaper editor Danny Lockwood was "outraged" when armed police arrested him in connection with suspected hate crimes against Ms Sherriff. He has been ruled out of the investigation.
Ms Sherriff said she has been targeted for far-right abuse daily, sometimes suffering hundreds of such incidents in a week.
Her staff have had to put safety procedures in place around her Wellington Road office, such as going to lunch in pairs.
She also said West Yorkshire Police had not taken her complaints of abuse and threats seriously.
The MP said she had "no faith" in the force, despite her father being in the police.
"My trust in the police has been really eroded," she said.
Gerry Wareham, chief crown prosecutor for Yorkshire and Humberside, said: "We considered this case carefully but the evidential test was not met to prove a criminal offence so we could not prosecute. The suspect was issued with a harassment warning.
"We understand Ms Sheriff's concerns and take any potential threat of this nature very seriously. We have offered to meet with her to explain our decision in full."
West Yorkshire Police said: "We can confirm a complaint has been received in relation to the police handling of an investigation into incidents in July and August 2018, when offensive material was left outside the constituency office of a local MP.
"This matter has been referred to the Independent Office for Police Conduct who are conducting an independent inquiry."
The force said the "tragic murder of Jo Cox in 2016 further emphasised the risks our MPs can face and West Yorkshire Police regularly reviews security arrangements, in accordance with national protocols".
"West Yorkshire Police has local processes to ensure there is an effective response to any threats made towards or concerns raised by local MPs."