These buses were plying without valid route permits, without registration certificates, road tax documents and some even had fake number plates among other irregularities, the bureau's chief director B K Uppal said.
He said illegal plying of private buses was a chronic problem for the state undertakings.
"On the instructions of the Punjab chief minister, the Bureau formed special teams and conducted checks of all passenger buses to curb tax evasion and other irregularities," he said.
"Out of the 1,715 buses, 1,261 buses were found plying with valid documents. In some cases the drivers were carrying photocopies of route permits whereas it was mandatory to carry the original.
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"Many private buses were not running as per the fixed time-table and some were using number plates of buses having valid route permits," he said.
Uppal also said it was clear that many buses were plying on a single route permit and he wondered if some non-AC buses were being plied on the route permits of AC buses causing tax loss.
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