An MP threatened to send naked pictures of a woman to her family because she was jealous of her friendship with her partner, a court has heard.
Claudia Webbe, 56, also allegedly called 59-year-old Michelle Merritt "a slag" and made a threat against her involving acid during a campaign of harassment between September 1 2018 and April 26 last year.
The Labour MP, who appeared in court on Monday wearing a black skirt suit, denies harassing Ms Merritt.
Susannah Stevens, prosecuting, said Webbe made a string of short silent phone calls from a withheld number to Ms Merritt, who told the court she had known Mr Thomas for more than 15 years and were "good friends", having previously dated.
She added: "The reason for the harassment appeared to be the fact that Ms Merritt was friends with Lester Thomas and this was an issue for the defendant, Ms Webbe."
Ms Stevens said the calls tended to occur when Ms Merritt was with the MP's boyfriend, Mr Thomas, and that they would be silent calls of short duration.
Ms Merritt gave evidence from behind a screen, saying: "There was a pattern that whenever I had even met with Lester Thomas, if we had gone out for a drink or something, there would be a phone call.
"When you are being called and no one answers, it's unnerving, especially as a woman who lives alone."
She said that on one occasion, on 11 October 2018, the call was made from a number that could be seen.
The court heard that when Ms Merritt put the phone number into Google, she discovered that it belonged to Webbe because the MP's number appears on Labour literature and also a Leicester Council website.
Despite being confronted by Ms Merritt's friend, Gill Smith, and told to stop calling, the court heard that the harassment "escalated in form" from this point onwards.
On Mother's Day, 31 March 2019, the defendant spoke to Ms Merritt during the phone call that she made and identified herself as Claudia.
Webbe queried why Ms Merritt was in touch with her boyfriend and that she was reportedly in "such a state" that she went on to call Ms Merritt a "slag" and said she should "be acid".
The prosecutor said Ms Merritt was "caused considerable distress by this call" and that she was "alarmed and concerned for her safety".
Ms Merritt reported the incident to the police and an officer told Webbe in April 2019 that she must not have any further contact with her.
But despite being warned by officers to stop calling, Webbe allegedly made a total of 16 further calls to the complainant, including one on April 25 last year, which Ms Merritt recorded.
The MP accepted telephoning Ms Merritt in a prepared statement she provided to police on 30 July 2020.
The court heard that Webbe told the police she did not appreciate that her phone calls would be unwanted nor that they were causing Ms Merritt distress.
Webbe denied making any threats to Ms Merritt on Mother's Day in 2019.
However, in the recorded phone call, the MP had made similar threats of revealing naked photographs to Ms Merritt's family and she later accepted that that was her on the recording.
Webbe, from Islington, north London, stood in the dock wearing a black suit, to confirm her name, date of birth and address, before sitting next to her solicitor as the case against her was opened. She denies a single count of harassment.
Webbe entered the Commons in December 2019, winning the seat formerly held by Keith Vaz, the Labour veteran who retired from Parliament in the wake of a scandal.
She was a councillor in Islington between 2010 and 2018 and was a member of Labour's ruling National Executive Committee. Earlier in her career, she was a political adviser to then-London mayor Ken Livingstone.
The trial, which is due to last one day in front of Chief Magistrate Paul Goldspring, continues.