this interview with retired Supreme Court Justice Wajihuddin Ahmed. The interviewer is Mian Abrar. Excerpt:
Question: What are your views about the Supreme Court’s reservations regarding the 21st amendment and military courts? Does the Court have the power to reverse parliamentary amendments in all other democratic countries?
Wajihuddin Ahmed: Yes I think the courts have the power to examine the constitutional amendments passed by parliament. The court also has the power to strike down any amendment which is in violation of the fundamental structure or framework of the constitution.
Remember this is not a constituent assembly which can pass any kind of amendment. This parliament does not have the power to unmake the constitution. The constitution has been made by the founding fathers in 1973 and there was a national consensus for making the constitution. There was a compact between the federating units and once it was achieved, the constitution was made.
Now every other parliament has the power to amend the constitution for day-to-day purposes, arising from time to time, but parliament cannot unmake the constitution.
There are dos and don’ts of amending the constitution. You can amend it under doable clauses but you can’t make amendments in the constitutional limits which fall under don’ts.
For instance, if parliament wants to amend the constitution to turn the parliamentary form of democratic system into a monarchy, it can’t do it.
If the majority of the feudal class in a routine parliament desires to take away all the fundamental rights of the people at large which are enshrined in the constitution, they can’t do it.
If the  feudals in the parliament want to do away with the judicial organ of the state, they can’t do it. It is in the parameters of the don’ts. Changes in basic structure of the constitution can’t be made.
I say so because a particular national assembly is elected on the basis of the manifesto they presented to the masses. If they sought the public mandate on the premise that they wanted to amend the basic structure of the constitution, and they win majority, then they could do it. The 18th and 21st amendments have to be vetted on this touchstone.
The Supreme Court has also intervened in the past whenever dictators and autocratic rulers wanted to amend the constitution according to their whims. It happened even though the constitution provides a procedure to bring in amendments.
In the context of the 18th constitution amendment, when it was passed by the parliament, there were some specific amendments about the process of appointment of judges. However, the Supreme Court convened an emergency session and the amendments were examined and referred back to parliament for a review as the amendments were made to change the basic structure of the constitution. So, finally, parliament referred to the reservations of the court and corrected the amendment process.
Now in a country like Pakistan such situations arise often. If any military dictator wants to amend the constitution as per his own whims, the courts intervene. But in India, there was one such intervention when an emergency was imposed by the then Prime Minister Indira Gandhi, when a question was raised whether the Indian Supreme Court could reverse the constitutional amendment? The Indian Supreme Court said it would do it if the basic structure of the constitution was amended.
Under Nawaz Sharif, the Supreme Court had also issued a stay order against parliament not to make amendments which are against the basic structure of the constitution.Competing views can be found here. The case for upholding the 21st Amendment seems to be three-fold: (1) the Supreme Court cannot invalidate a validly enacted constitutional amendment; (2) the civilian courts are not working; and (3) after all, it's only for two years.