The Major League Baseball Players Association is worried about the effects wearable use on and off the field will have on players.

It follows the MLB approving two wearables, the Zephyr Bioharness and Motus elbow sleeve, which log heart-rate and strain on arms, respectively.

See Also: What happened when the NFL found IoT?

Some union representatives and players have argued that wearable data collection could be used to bench players that don’t get enough sleep or have a bad day on the practice field. Others suspect that MLB teams may use data to lower the contract value of players.

New York Mets Curtis Granderson, a MLBPA representative, said: “It’s a matter of how much access will we have to it?’ How much [access] will the team have to it? What will be done with it?”

Several players voiced similar concerns to Vocativ’s Joe Lemire about the longevity of data collected and how it can be used by MLB teams. In the current state, coaches look at the data post-game and evaluate performance and health.

MLB players worried about off the field monitoring

Players are also concerned that teams will force them to wear the devices outside of work, to track their health and fitness at home. This could seen as a major invasion of privacy. Rockies catcher Nick Hundley said that it may lead to a Philadelphia Eagles situation under Chip Kelly, where most of the team left during the two years due to invasive technologies.

MLB is trying to ensure unions that evaluation of performance or health risks will not come up during contract signings, but players seem to not believe the directors in charge of making the game fair for players.

If a team fails to provide adequate data protection, it may lead to players asking to be removed from the team or taking the wearables off during games. MLB players have already expressed certain disdain for tech entering the game, and this season will be jam packed with wearables to add to all of the technology already assessing player’s capabilities.