Is this good for guinea pigs?

I have 2 guinea pigs, and we just got pine pellets for them, and we read their perfectly healthy. But in the past couple days we've seen them chew on the pellets *theres dust left behind and we thought it was their urine but it isn't cause those things don't dissolve* and we even saw one of them chewing on it and we stopped him. Is this bad for them if they ingested them? Is there anything I can do to stop it? I won't be able to get other pellets for 2 weeks, cause we went to 2 different stores and they don't have have the ones we usually get, and they both said 2 weeks for stocking. Please help? thank you.