Union in entity framework

I have two tables: Vehicles and Workers.

Vehicle(Id, Number)
Workers(Id, Name, ContractorVehicleNumber)

I would like to write lambda query to return all the vehicles and the contractor vehicles. Something like in sql:

SELECT Id, Number
FROM Vehicle
UNION
SELECT NULL, ContractorVehicleNumber
FROM Workers

This is what I made:

public IQueryable<Vehicle> Get(bool includeContractorVehicles)
{
    IQueryable<Vehicle> query = GetQuery();

    if (includeContractorVehicles == true)
    {
        WorkerRepository rep = new WorkerRepository();
        IQueryable<Vehicle> contractorsVehicles = rep.GetWirkers().
            Select(x => new Vehicle()
            {
                VehicleNumber = x.ContractorVehicleNumber
            });
        query = query.Union(contractorsVehicles);
    }

    return query;
}  

But I get an exception:

The entity or complex type 'XXXXXXXX' cannot be constructed in a LINQ to Entities query.