Klingons

Klingons are alien species. They have neutral zone with Earth.

Chukspace encounter
After Chukspace successfully destroyed Agmat's rockets which targeted macaws, it jumped to Klingon neutral zone, in system k-81, sector 018-0. Klingon Battle cruiser attacked Chukspace and Chukspace returned fire. Then, Chukspace retreated. (About Older class revolution 3)

Alternate timelines
In one alternate timeline, created by Bohandi using time-weapon, Klingons resisted Bohandi and helped Ansoids and Greys attack Coridiana system. (Aliens)

Background
Klingons are, in fact, species from Star Trek. Non-canon Works (and Troubles in journey, half-canon) stated that Stat Trek is a Parallel universe.