The Liberal government has introduced tough new measures aimed at protecting sexual-assault complainants from intrusions into their sexual past, the first strengthening of the rape-shield law in a quarter-century.

In a Criminal Code amendment that a sexual-assault crisis centre called a direct response to the acquittal of broadcaster Jian Ghomeshi last year, proposed legislation would spell out for the first time that a complainant's text messages, e-mails and video recordings with sexual content or a sexual purpose can be kept out of trials. A new provision would subject these messages, including those sent after an alleged assault, to the same rules as evidence of a complainant's past sexual activity: requiring a judge's advance approval after a closed hearing for them to be used in a trial.

A second change would prevent personal records of the complainant that are in the accused's possession, such as journals or diaries, or medical records, or perhaps personal letters, as in the Ghomeshi sex-assault trial, from being used as evidence unless a judge agrees in a private hearing. The same process is currently used when an accused seeks access to records held by third parties, such as psychologists or rape-crisis centres.

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"Women who work with us were very discouraged after what we saw in the Ghomeshi case," Hilla Kerner, a spokeswoman for the Vancouver Rape Relief and Women's Shelter, said in an interview.

The provisions in the new bill send a message that "your past, the things you did before the attack and after the attack, will not deter the criminal justice system from actually dealing with the attack and holding men accountable."The government would also, for the first time, say in law that complainants have the right to legal standing when a court is considering an accused person's request to introduce evidence that is protected under the rape-shield law – that is, to have a lawyer make arguments, separate from those made by the prosecutor, on the complainant's behalf. Judges would have to inform each complainant of this right. (Complainants could not appeal if they lose the argument.)

Justice Minister Jody Wilson-Raybould said she hopes the proposed changes "will go a long way towards ensuring that complainants are treated with the compassion, dignity and respect they deserve." But defence lawyers say the bill is deeply unfair to accused people and will be subject to widespread constitutional challenge.

The changes arrive in an environment of heightened public attention to the issue of whether victims of sexual assault can find justice.

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The Globe and Mail revealed this year that some police forces have a high rate of cases classified as unfounded. A series of high-profile sexual-assault trials have raised concerns about the difficulty of securing convictions, women's willingness to trust the system and judges' knowledge of the law. These include an Edmonton trial in which a judge locked up a complainant to ensure she would testify, a Calgary trial in which a judge asked a complainant why she did not keep her knees together, a Halifax trial in which a judge found a taxi driver not guilty although he engaged in sexual activity with a severely inebriated passenger and Mr. Ghomeshi's trial in Toronto, in which the acquittal turned in part on after-the-fact communications between multiple complainants and the accused.

But during that period, criminal defence lawyers have raised concerns about a rush to judgment and some appeal courts have thrown out convictions, ruling that judges were unfair to defendants. And some criminal defence lawyers say the Liberals' new bill, which must be debated in Parliament and voted on before becoming law, would dangerously alter the balance between the accused and the prosecution. "The message that's being sent by the government is that people who are charged with sexual assault are guilty," lawyer Joseph Neuberger of Toronto said in an interview. "The extent to which they are going to restrict cross-examination in this area is unbelievable, as compared to every other offence in the Criminal Code."

Edmonton criminal defence lawyer Nathan Whitling, vice-president of the Alberta Criminal Trial Lawyers' Association, said in an e-mail that broadening the definition of "sexual history" to include communications of a sexual nature would require disclosure of those materials to the Crown and the complainant.

"This would be contrary to the current rule which is that the defence is under no obligation to co-operate or assist the Crown by providing any documentary evidence to the Crown or the complainant in advance of the trial," Mr. Whitling said. "In the Ghomeshi trial, these rules would have required the defence to disclose the text messages and photographs to the Crown and the complainants in advance of the trial, which would have enabled them to adjust their testimony to make it more consistent with its contents."

The justice department said the changes to the law were not based on any particular case, but on a thorough review of a series of cases.

Marie Henein, a Toronto lawyer who represented Mr. Ghomeshi, said she was unavailable to comment on Tuesday.

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The government also made changes intended to clarify the law as previously interpreted by the Supreme Court and other courts. For instance, an unconscious person cannot legally consent to sexual activity; and consent requires an affirmation, in words or actions. The bill contains nothing intended to clarify consent in cases of inebriation short of unconsciousness.

University of Ottawa law professor Elizabeth Sheehy and Allard School of Law professor Emma Cunliffe called the right of legal representation in rape-shield hearings an important step, but said it will be largely ineffective unless provincial legal-aid programs provide financial support to complainants seeking to retain a lawyer.