A verse often appealed to by Unitarians is the one in which Jesus refers to the Father as the "only true God" in John chapter 17:
John 17:1-3
1 These words spake Jesus, and lifted up his eyes to heaven, and said, Father, the hour is come; glorify thy Son, that thy Son also may glorify thee:
2 As thou hast given him power over all flesh, that he should give eternal life to as many as thou hast given him.
3 And this is life eternal, that they might know thee the only true God, and Jesus Christ, whom thou hast sent.
Unitarians appeal to the above verse, because if Jesus refers to the Father as the "only true God", then it follows that there are no others who are the "true God". It is an eisegetical reading to suggest that Jesus actually was saying that the Father, and Himself, and the Holy Spirit are the "only true God", especially when in the passage, He distinguishes between the one He is referring to (God), and Himself, and says that He was sent by the "only true God". This is not how one speaks if they intend to communicate that they are God, because it communicates very clearly that they are not God, and that they are distinct from the only one properly called "God" in the absolute sense.
There are two verses that are most commonly appealed to from the Trinitarian point of view in response. First, sometimes it is asserted that Jesus is called "true God" in 1 John 5:20. However, closer examination of that passage demonstrates that this is a misreading, and that the Father is being referred to there as well.
The other verse commonly used in response is Jude 1:4:
Jude 1:4 (LSB)
4 For certain persons have crept in unnoticed, those who were long beforehand marked out for this condemnation, ungodly persons who turn the grace of our God into sensuality and deny our only Master and Lord, Jesus Christ.
Above, Jesus is called "our only Master and Lord". Therefore, it is argued that if Jesus here is called our "only" Lord, and yet God the Father is clearly our Lord as well, then it is an error to draw the conclusion that "only" in John 17:3 excludes Jesus Christ.
Firstly, it should be noted that there is a textual variant in this verse in Jude that affects this discussion. Some manuscripts read, as the KJV translates, "the only Lord God, and our Lord Jesus Christ" for the end of the passage. If this is the original reading, then Jesus would not be called the "only Lord" here. However, nearly all modern Bibles reject this variant as an addition, and thereby assert that the better reading is the one represented in the LSB above.
Therefore, Jesus is called our "only Lord" in this passage. However, asserting that Unitarians who appeal to John 17:3 would make this passage exclude God the Father from being the Lord is a misunderstanding of the position of "Lord" established in the New Testament.
It is a teaching of the New Testament that Jesus has been placed into the position of "Lord" by God (1 Corinthians 15:27-28), as the Apostle Peter says:
Acts 2:36
36 Therefore let all the house of Israel know assuredly, that God hath made that same Jesus, whom ye have crucified, both Lord and Christ.
Peter says that God has made Jesus both Lord and Christ. As a result, the confession of Christians in the New Testament concerning the positions of God and Jesus is as follows:
1 Corinthians 8:6
6 But to us there is but one God, the Father, of whom are all things, and we in him; and one Lord Jesus Christ, by whom are all things, and we by him.
Above, notice the two distinct positions - God, occupied by the Father, and Lord, occupied by Jesus. The position of "Lord" is one established by the Father for Jesus, and is a position under God, who is the "head of Christ" (1 Corinthians 11:3).
Therefore, Jesus is our "one Lord" or "only Lord", and is distinct from our "one God". That does not mean that the Father is not the Lord in the absolute sense, or that Jesus's Lordship is not ultimately derived from God, and subordinate to God. Rather, both this passage, and Jude 1:4, are teaching the doctrine that Jesus, for Christians, occupies a unique and exalted position - "Lord" (and "Master").
However, returning to John 17:3 - the position of "God" is not something created by another, above the Father, for the Father to occupy in some subordinate way, or sense. Instead, the word "God" in John 17:3 describes a position which can by definition (assuming the Biblical doctrine of Monotheism) only be occupied by one - the necessary and eternal Being responsible for the universe's creation. There is only "one God", and as Jesus says in John 17:3, it is the Father, and Jesus is the mediator between that God and humanity (1 Timothy 2:5).
Therefore, Jude 1:4 is not denying that the Father is our Lord and Master. It is instead referring to a position that God has created for Jesus Christ, and placed Him in - that of "Lord". He is our only Lord, under the only God.
John 17:3 is a simple, straightforward affirmation by Jesus that the Father, in distinction from all others, is the "only true God". And, because there is only one God, this means that none other besides the Father are God, in the sense referred to in the verse. The fact that Jude 1:4 refers to Jesus as our "only Master and Lord", in contrast, does not exclude God the Father from being the ultimate Master and Lord, as it is referring to exalted positions in which God has placed Jesus.