Kerry McCarthy says she suffered unwanted attention from fellow Labour MP Kelvin Hopkins spanning 20 years and found it "upsetting".
The former shadow environment secretary is the first MP to make specific claims of inappropriate behaviour since the Westminster scandal erupted.
Ms McCarthy said the Luton North MP sent her a series of letters and cards about her appearance, including one in which he described having a dream about her.
But Mr Hopkins said Ms McCarthy's complaint had caused him "immense personal hurt and utter dismay" from someone he counted as a friend.
He added: "I cannot understand why a Parliamentarian of such experience and standing, who is also such a long term friend, would not have told me that she was unhappy with any aspect of our friendship rather than going straight to the national press.
"At a minimum I would have expected a Parliamentary colleague to raise any complaint through normal channels, allowing me due process and a fair chance to defend myself, if necessary."
Ms McCarthy said she decided to go public after activist Ava Etemadzadeh complained last week about the behaviour of Mr Hopkins.
He was suspended by Labour after Ms Etemadzadeh contacted the party again with fresh information following an initial complaint over dealings with the MP in 2014 and 2015.
Mr Hopkins was reprimanded at the time by the-then chief whip Dame Rosie Winterton but was appointed shadow culture secretary in 2016.
He "categorically denies" any inappropriate conduct in relation to Ms Etemadzadeh.
Ms McCarthy, 52, first met Mr Hopkins, 76, when she was in her late 20s and they were both involved in Labour politics in her home town of Luton.
In 1994, when she was chairwoman of Luton North constituency Labour Party (CLP) and he chaired Luton South CLP, they went out for lunch, with Ms McCarthy believing it was to discuss political issues.
He later sent her a card saying he had invited her "because you are attractive, intelligent and charming" before urging her to "dispose" of the note, she said.
In a second note, Mr Hopkins enclosed a photo of Ms McCarthy and described her as "pretty" before again asking her to dispose of it, she claimed.
He also sent a postcard, which appears to be dated 1996, in an envelope to her place of work, asking whether her employer specialised in "pretty, petite brunettes".
Ms McCarthy said she went to another lunch with Mr Hopkins because she found it awkward to say no to the invitation. He sent a card afterwards suggesting it "would be nice to meet again".
On another occasion, also believed to be in 1996, Ms McCarthy said Mr Hopkins placed his hand on hers when she was not looking as she was getting out of a car.
A note sent in the run-up to the 1997 general election said: "You know I think you are lovely ... but I never see enough of you ... after May 1st perhaps ... K x."
The letters then stopped until her 50th birthday, when Mr Hopkins sent a note on parliamentary writing paper to mark the occasion. By this time Ms McCarthy was an MP.
A final letter was sent some time in 2015/16 but it is not clear if it was written after he was reprimanded for the incident involving Ms Etemadzadeh.
In it, he described having a dream about Ms McCarthy and said she remained a "very attractive woman", according to Ms McCarthy.