Your project just completed, and one of your subcontractors has sent you floor seats to the next big tennis game to thank you for your business.

Thank you.

It's not a right to accept any form of free stuff to influence your decision in anyway on a current or a future project.

I would ask him to take it back. 

i will refused

i have a money to go when i need

i don't like any mystery relationship in my work

You have to refuse his invitation and reply him with a polite "Thanks but not".

When someone accepts this kind of "gifts", that person is becoming into a corrupt person.

In Spain, there have been a lot of wrong and indecent practices as your question indicates;  these kind of "friendships" between politicians and building companies have resulted in a lot of corruption cases that are going to try them for these practices among others.

Refuse and thank him.

Thanks,

Refuse his invitation and thank him.

Thank you my dear brother ,,,,  I think that the best answer (  refusal ) because the contractor seeks to build a relationship with the resident engineer in anticipation of future work exploits them achieve their interests by building that relationship with the Resident Engineer and there are words saying ( Feed the mouth, shame the eye  ) and ask the contractor was it will direct you to such a call if you sitting at home or anywhere else away from his work  ????? Surely he does not do it  !!!!!!!!!!

I agree, it is not acceptable/ethical to except such a gift.

In many cultures however it is an insult and you have to be careful how you decline such a gift..

You can say "thank you but I can not except this gift, due to company policy".

You can go to your HR department and tell them about it to get advice how to handle this situation best... You also could tell the contractor to donate a gift to a charity......

It all depends on the culture and customs .. you do not want to insult any one... and if there is a question get some guidance how to handle it!

Thank you for invitation>>>

First i will thanks him a lot then i  will refused>> 

Refuse the offer and tell him that it can be considered as a bribe.

Recommended to Refuse.

Most corps set a maximum value amount on gifts if you go above it you are in violation. If the value exceeds, you must Thank, Refuse & report. Otherwise can be considered for building relations. Rejecting an inexpensive gift may be taken as an insult.

Still always better to be in Professional relationship. Never build them into personal.

Unacceptable behavior