The state roadways concerned are being issued notices about their buses failing the PUC test, said a transport department official.
The PUC is a certification mark issued to motor vehicles in India that meet emission and pollution control norms.
The official said that 50 buses belonging to state roadways of Haryana, Uttar Pradesh, Himachal Pradesh, Uttarakhand, Chandigarh, Punjab and Rajasthan were checked and 24 vehicles failed the PUC test.
Ten of the 13 buses from UP were found not complying with PUC norms, while the 17 buses from Haryana, seven failed the test, he said.
The buses that failed the PUC test will not be allowed to enter the ISBT unless they obtain fresh PUC certificates, the official said.