(Sorry, I'm new) AGAINST
Labor unions are beneficial to the economy because they help the workers that take part in them feel secure in the fact that they have a job. This encourages workers to stay within their companies, which supports the economy by keeping jobs. In this, it also acts as an attraction to taking a job with a union behind it. If people want to take those jobs, it will help the economy.
They're also beneficial to the economy because it helps keep wages at a normal rate for the workers. If unions did not exist, the employers would have complete power over the wages of the workers. Most likely, the employers would lower the wages to put more money in their pockets, and less in the pockets of the 'common man.' When most of the money is in the hands of few, the money flow in the US economy indefinitely slows because the money being spent by the common consumer is now being hoarded by a few people. Less money in the pockets of the workers means less money being spent, and that weakens the US economy.