Plexus Corp. (NASDAQ: PLXS) is getting crushed in the after-hours. The company announced a “disengagement” as a supplier to Juniper Networks Inc. (NYSE: JNPR). In short, Juniper has terminated its relationship. Plexus said that the exact timing of the transition away is not yet known but it did go on to say that it is expected to occur by the end of its current fiscal year.

Plexus said that this was very surprising news considering recent communications and activities with Juniper after having been a supplier to it for more than a decade. Its CEO said, “While this is a significant event for us in the near term, our new business wins of $956 million during fiscal 2012, including in the networking/communications sector, provides us continued optimism in our strategy.”

The damage is harsh now that shares have reopened. After a 1.2% gain to $27.96 today, the shares are indicated down 21% to $21.90 against a prior 52-week low of $23.23 to $38.50. Plexus was downgraded by Deutsche Bank to Hold from Buy back on October 26 based in part upon already-lowered guidance.

Plexus has only traded 35,000 shares since the close but it is down worse than any tracked NASDAQ stock.

JON C. OGG