Local media reported that five graduates from Espanyol's youth academy had recently joined Barca and Collet told a news conference on Friday the club would be taking steps to make sure it did not happen again.
"For a start, staff and coaches from other clubs will not be allowed to watch training sessions if they do not have permission or a prior appointment," he said.
"And we will oblige players selected by the coaching staff to sign a training contract," he added. "We are not here to produce players for other clubs."
Players who left without making sure Espanyol were involved in talks with their new club would not be allowed back, Collet said, and called on the professional league (LFP) to act to prevent clubs poaching youngsters.
Many Spanish clubs have highly successful academies and those of Espanyol and Barca are considered to be among the best.
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