"I will be buying an AR-15 tomorrow, because if you impeach MY PRESIDENT this way, YOU WILL HAVE ANOTHER CIVAL WAR!!! #MAGA2020”

This is what MLB umpire Rob Drake's Twitter account posted and quickly deleted on Tuesday night, according to ESPN ... and now the league has launched an investigation into the situation.

Drake -- who has been outspoken over his frustrations with the House of Representatives impeachment proceedings with President Trump -- has since deactivated his Twitter account.

Before tweeting his plans to buy the assault rifle, Drake also said "You can't do an impeachment inquiry from the basement of Capital Hill without even a vote! What is going on in this country?" earlier in the day.

FYI -- Drake umped his first MLB game in 1999 and joined the league's full-time staff in 2010. He's been involved in many major events including the All-Star Game and playoffs, although he is not on the current postseason roster.

It's important to note -- Drake didn't break any laws with what he said, but clearly the tweet is concerning enough from a PR standpoint that the league wants to get in front of it.