Apartment escalation

Hi Experts,

At the time of launching of an apartment project the builder was fixed the two BHK apartment price at Rs.20 lakhs.  Till now the builder has completed only 70% of work.  Now can builder charge Escalation and collect money from customers, If yes on what basis he can collect, If not Why he cannot charge escalation.

[Note:Escalation Clause is not there in the Sale Agreement]