Technical Solution
if you're using Team System you could use checkin policies to enforce it. Other versioning systems no doubt support similar things. You'll need the TFS Server Power tools for this.
Non-technical
Aside from a technical solution you might want to explain the reasons you're requireing these coding standards (quality, legal etc.). They might feel the policy is overly restrictive or simply do not understand the necessity.
If you can convince them of the need to do this, you no longer will have to force them.
