Megan McArdle:

Obama signs an executive order encouraging stimulus projects costing more than $25 million to use union-only project labor agreements. This means that any contractor or subcontractor working on a large project will have to submit a bids with collective bargaining agreements spanning one or more unions for the duration of the project. In theory, you could bid a job with non-union labor, but let a union run the bargaining. In practice, projects with PLAs almost always go to union shops.