What are the rules on receiving communion in other churches?

[fishonfridays]

If a close relative is getting married say for example in a Lutheran Church and they ask you if you would receive communion. As a Catholic is it a mortal sin to receive communion in another church? What are the rules in this matter?

 

[Devon_Caffran]

These links should be helpful for understanding why Catholics should not take communion in non-Catholic services. If you have any further questions or concerns that are not answered by these links, please contact Catholic Answers directly.

**Recommended Reading:
**What should I do in a non-Catholic church?
%between%Is it a sin to receive communion in a Protestant church?
Ecclesia de Eucharistia (Note especially sections 43-46)