PORTLAND (AP) — The Pacific Northwest Christmas Tree Growers Association says it has found a document that proves Mexican inspectors held up the delivery of trees last season for protectionist reasons.

Oregon leads the U.S. in Christmas tree production, and roughly 13 percent of the harvest is sent to Mexico. Last Christmas season, the trees crossed the border with ease, but often ran afoul of aggressive local inspectors, who held up tens of thousands at a time, increasing business costs.

The stated reason for the delay was needle midges and twig weevils.

But Bryan Ostlund, the executive director of the tree growers’ association, said those common pests are not serious threats, and noted that inspectors ultimately pulled only 220 trees off the market.

Ostlund suspected something else was going on. Recently, he came across a document on the Internet that he considers incriminating: a 2007 Mexican parliamentary committee resolution that called on officials to block Oregon trees to protect the local industry.

The resolution, signed by two dozen lawmakers, said imports drain pesos that Mexican growers could earn if they were able to produce more trees. It also cited the ecological benefits of growing trees in Mexico.

“If I’d had this document prior to the 2007 shipping season,” Ostlund said, “I would have known exactly what we were dealing with.”

Oregon produces between 7 million and 8 million trees a year, and Mexico buys about 1 million of them for an estimated $20 million, Ostlund said.

Mexico has been trying to get its own Christmas-tree industry off the ground, planting a Douglas-fir variant. So far, however, Mexican growers have fallen well short of supplying the nation’s needs.

Ricardo Alday, a Mexican embassy spokesman in Washington, D.C., told The Oregonian newspaper Thursday that he was not familiar with the issue but would check into it.

To help preserve their sales to Mexico, Northwest growers have enlisted the help of federal agriculture officials and a public-relations firm.