Trade officials in the Philippines on Monday said they were closely monitoring trouser exports to the European Union after a probe discovered some local firms were falsifying the origin of apparel made in other countries.

The Department of Trade and Industry said including a "Made in the Philippines" label on garments made overseas affected the wages of workers in the $3 billion industry and its foreign quotas.

The investigation was launched after trouser exports to the EU rocketed almost 150 per cent in the first two months of this year from the year prior.

"This activity is usually instigated or orchestrated by unscrupulous brokers who encourage and teach willing companies to fabricate fraudulent documents," it said in a statement.

It added the probe had found "certain companies actually have no production operations, while some were unable to show the goods that were supposed to be shipped to the EU countries".