China has protested for India building a bridge across the Galwan River,even China is building roads and air bases in the border area.For this reason only the dispute has started since from May. In June, Chinese went on to put up a tent near the LAC. That is why the clash happened on Monday.

The Chinese objection is that the Darbuk-Shaykh-Daulat Beg Olde Road (DSDBO) is about 255 kilometers long. Which is very Important for India,because it reduces travel time between Daulat Beg Olde Air Base from 2 days to 6 hours.
The highway passes along the Galwan River and the actual boundary line. The construction of the highway will help the army to carry its goods.
The Aksai Chin area, along the Karakoram Highway between Xinjiang and Tibet, will also be adjacent to this India-made road. If the war breaks out, it will be able to send its troops to India.
That is why the China was obstructing the road work