Vail police are again warning skiers and snowboarders of a growing trend of fraudulent lift ticket sales this season that has cost visitors thousands of dollars.

So far this winter, there have been 39 such cases reported to police, an 875 percent increase over the 4 cases during the same period last year.

“As a reminder, using another person’s ski pass can have criminal consequences and potentially bar the unauthorized user from skiing the entire season,” Vail police said in a news release Wednesday. “Once fraudulent use is identified, suspects are either issued a summons into court and released or arrested, depending on the circumstances.”

Using a fraudulent lift ticket carries a maximum fine of up to $999 and 180 days in jail.

Ski pass fraud on the rise. Always purchase VR ski passes directly from Vail Resorts or authorized retailer. Details https://t.co/CdBsjjDQde — Vail Police (@VailPolice) February 22, 2017

A single-day, adult lift ticket at Vail on Wednesday was $189.

In January, Vail investigators said they were seeing tickets being unlawfully sold online — on sites like Craigslist — by third-party vendors through a scam targeting out-of-town visitors. Police say when potential buyers arrive at the resort to pick up their tickets, they are either non-existent or fraudulent.

In one case, police say, a fraudster purchased $2,000 worth of lift tickets from Vail Resorts and then resold them to a group via Craigslist. When the buyers went to use the tickets, they found that the passes had been flagged for insufficient payment.

Authorities say it turned out the fraudster had reported the credit card he used to purchase the tickets as stolen.

Vail Resorts is the only authorized retailer of ski passes on Vail Mountain.