The SCA applies to a lot of federal service contracts above a certain dollar amount and sets a wage and benefit floor, by labor category and location, that you have to pay covered employees, through a wage determination attached to the solicitation. It covers things like janitorial, food service, and administrative support work more often than highly credentialed professional labor, though coverage depends on the specific labor categories involved, not just the industry. Price your labor below the SCA floor and you are noncompliant, so pull the wage determination before you build your cost estimate, not after.

In a sentence

"This contract is subject to the Service Contract Act; the applicable wage determination is incorporated by reference." Your labor pricing has a legal floor before you write a single number, so find and read that wage determination first.