According to the constitution of Pakistan, no law can be promulgated which is in explicit violation of Quran & Sunnah, and as per Islamic law, the man does not need permission of current wife (wives) for marriage. He can marry up to four without any fear.
The Muslim Family Ordinance Law 1961 is
not in contradiction with the Holy Qur'an as the Holy Qur'an does not prohibit seeking permission (from the council) for second (or subsequent) marriage. Nor does the Holy Qur'an forbid to delegate the power of divorce to wife, or curtail Husband's power of divorce (as is
legal under Muslim Family Ordinance of 1961)
And yes, the Constitution of Pakistan states that no law shall be enacted which is repugnant to Injunctions of Islam. But the same constitution, through article 203, has empowered/established the Federal Shariat Court (and the Shariat Appellate Bench of the SC) as the
only institution that has the authority to examine and decide the question whether or not any law or provision of law is repugnant to the injunctions of Islam..... And the Federal Shariat Court has already decided (Jan 5, 2000) that this law (i.e. Section 6 of 1961 Family Ordinance) is NOT against the teachings of the Holy Qur'an .
Shariat Petition Nos.26/I of 1994, 2/P of 1996 and 2/I of 1996 were filed to challenge the validity of section 6 of the Muslim Family Laws Ordinance, 1961 as opposed to the Injunctions of Islam.
The Federal Shariat Court, after hearing the detailed arguments, ruled:
" ...we would hold that subject to our observations and recommendation in para.92 to amend the provisions of section 6 of the Muslim Family Laws Ordinance, 1961,
the said provision, are not violative of the Injunctions of Islam."
The detailed judgement of FSC where this argument/contention (that the Muslim Family Laws Ordinance, 1961 is violative of Islamic injunctions) is thoroughly discussed and summarily refuted :
https://gmlaw.wordpress.com/2013/10...s-of-muslim-family-laws-ordinance-un-islamic/