Google has just updated the review content guidelines to explicitly prohibit review stations AND employee reviews.
The changes to the policy are noted in italics:
For instance, as a business owner or employee you should not review your own business or current place of work. Don’t offer money or product to others to write reviews for your business or write negative reviews about a competitor. We also discourage specialized review stations or kiosks set up at your place of business for the sole purpose of soliciting reviews.