Yep. It's true. And no, I'm not joking.
However, it's probably not the form of slavery you're thinking of.
No Kunta Kinte (not Toby) here.
Have a look at just a few of the texts:
No one can serve two masters, for either he will hate the one and love the other, or he will be devoted to the one and despise the other. You cannot serve God and money.1 Cor 7:22
For he who was called in the Lord as a slave is a freedman of the Lord. Likewise he who was free when called is a slave of Christ.Matthew 25:21
His master said to him, ‘Well done, good and faithful servant. You have been faithful over a little; I will set you over much. Enter into the joy of your master.’Romans 1:1
Paul, a servant of Christ Jesus, called to be an apostle, set apart for the gospel of God,The Greek word that is referred to in these verses is (or a form of) *(duolos) meaning: a slave, bondman, man of servile condition. Strong's Concordance further explains it as giving yourself up to another's will or interests.
Let this challenge you to further study what it means to really be a slave to Christ.
Here is one resource I have been recommended to read by @Sola5Girl and @lunchboxsw (read a review here)
What have you read that has encouraged your faith and led you to lead a life more bent on Christ's will and not your own?
Also, something to consider: How does our slavery to Christ affect our free will?