As India celebrated its 69th Republic Day, CPI-M General Secretary Sitaram Yechury on Friday said the basic tenets of the Constitution are "under grave threat"."Greetings to all of us citizens on Republic Day. It was a momentous day when India adopted values and principles, way ahead of the times. We must, now push them further ahead and ensure genuine Equality for each citizen," said Yechury in a tweet."Our Constitution was adopted on this day, 68 years ago. Its basic tenets and principles - the Right (along with Freedom) to Equality - are under grave threat today. We need to go beyond the levels of Equality and Fraternity achieved today, not regress," Yechury tweeted.