As senators race to pass a major bill to authorize the Federal Aviation Administration for the next five years, dozens of amendments have piled on, threatening to derail the legislation and raising concerns about the potential of a compromise ahead of the Friday deadline.

It has taken months for top lawmakers in both chambers to strike a deal on a 1,068-page aviation bill. Now, those who have not been involved in negotiations are looking for modifications, and in some cases, to add provisions unrelated to the overarching bill.