Train operator Northern was warning at around 5pm that services could be delayed by up to an hour - and even cancelled - because of culprits.
Around 30 minutes later, it said the line was open again but and cancellations are still expected.
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"Train services running through this station will be cancelled or delayed by up to 60 minutes."
They posted at around 5.30pm: "Following trespassers on the railway at Halifax the line has now reopened.
"Short notice delays and cancellations are still expected due to the number of trains and crew affected."
The delays may cause issues for Tom Jones fans headed to Halifax this evening to see the music icon perform at The Piece Hall.