Can you purchase workmans compensation for one construction job?
Yes, in New York. Purchase policy for employer and request it be cancelled after the job is done. Some construction companies form a new corporation for each job. If you do, obtain a policy, finish the job, dissolve the corporation and notify the comp carrier. If you are doing business in construction and will expect to have many jobs, it is cheaper and makes more business sense to buy a policy and simply keep it in force, since you are going to need it for the next job.
