AUSTIN, Texas—House Speaker Paul Ryan’s super PAC is for the first time this year pulling TV advertising time it reserved to back incumbent House Republicans facing tough re-election fights.

Mr. Ryan’s Congressional Leadership Fund is canceling about $1 million it planned to spend to back Colorado Rep. Mike Coffman and the $2.1 million it reserved for Michigan Rep. Mike Bishop.

“CLF will continue to run strong field operations in these districts and will continue to conduct polling and evaluate races across the country as we do everything we can to protect the Republican majority,” CLF spokeswoman Courtney Alexander said.

The cancellations suggest CLF may be pulling funds from candidates that seem less likely to beat their Democratic challengers.