To avoid the possibility of future disputes, you should obtain written confirmation of working conditions (a labor contract or company regulations), such as particularly wages, working hours, terms of employment, and other conditions. 
In principle, workers in Japan, regardless of nationality, are governed by Japanese labor laws and regulations such as the Labor Standards Law,  Minimum Wage Act, and Workmen's Compensation Insurance Act. For up to date information please see the Ministry of Health, Labor and Welfare's foreign worker's guidebook at www.mhlw.go.jp/english/org/policy/p43.html

Aichi Labour Bureau

Aichi Labour Bureau’s Assistant Counselor for Foreign Workers is open from 10:00 to 12:00 and 13:00 to 16:00 on Mondays and Thursdays for English interpretation and Tuesdays and Thursdays for Portuguese interpretation. Closed on holidays.
Hours: 10:00-12:00, 13:00-16:00
Closed: Weekend, holidays, and December 29 to January 3.
Phone: 052-972-0253
Address: Godo Chosha Building #2 2F, Sannomaru 2-5-1, Naka-ku, Nagoya 460-8507  

Access: a 3 minute walk from exit #5, Shiyakusho station, off the Meijo subway line
                                        
The Tokai General Union

The Tokai General Union also provides support to workers of any nationality who are experiencing workplace difficulties in Japan. They can help in cases of non-payment of wages, unfair firings etc. and negotiate with management to defend and improve conditions. If you are facing a problem at work or wish to know your legal rights, please feel free contact them. The General Union is an NPO and funds are limited, so those wishing to receive help are required to join and pay membership.

Languages spoken: English
Phone/ Fax: 052-561-8555
Address: NPO Plaza Nagoya, Meieki Minami 1-23-11, Nakamura-ku, Nagoya 450-0003
Website: www.generalunion.org/   E-mail: tokai@generalunion.org

Nagoya Nikkeis

This organization provides job introductions and consultation for foreign nationals of Japanese descent.
Hours: 09:30-16:30

Closed: Weekend, holidays, and December 29 to January 3.

Languages spoken: Portuguese and Spanish
Phone: 052-561-3781 
Address: Sumitomo Seimei Nagoya Building 14F, Meieki Minami 2-14-19 , Nakamura-ku, Nagoya  450-0003