According to reports, this resolution was brought into notice by State Minister, Tript Rajinder Singh Bajwa who argued that Guru Nanak Dev fought for equality throughout his life and ending this discrimination against women will only help his cause. 

As an end to years of discrimination, the Punjab Assembly unanimously passed a resolution urging the Akal Takht and the Shiromani Gurdwara Parbandhak Committee (SGPC) to allow Sikh women to sing hymns in the sanctum sanctorum of the Golden Temple in Amritsar.

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Bajwa also rejected an Akali leader’s claim that according to the Sikh religious code of conduct, Sikh women are not allowed to perform ‘Kirtan’ at the ‘Darbar Sahib and mentioned,

There was no mention in the Sikh history of any discrimination against women. But Sikh women were not allowed to perform Kirtan Sewa till now. Only Sikh men perform ‘Kirtan’ at the Golden Temple currently. 
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This welcoming change has come around the time of Guru Purab and it couldn’t have been any more auspicious.