Said out loud: "How can we squeeze this in without re-prioritizing or impacting other planned work? Are we sure it's all estimated correctly?"

Silently implied: "Spend more hours working. Alter existing estimates enough to fit it in."

You can ask them if they're asking for overtime/crunch and they'll say, "No, work/life balance is important to us at BigCorp. It's just that this is as important as our existing planned work and it would make our team/department look amazing if we can get this done too.". Yada, yada, yada. You can keep pushing back but how many times can you do that before you're no longer considered a team player?