Is there a balk in Majors?

No. In the Major Division and below, pitching violations are called illegal pitches, not balks. Balks apply from the Intermediate (50/70) Division up.

• No complete stop needed. At Majors and below, the pitcher doesn't have to come to a complete, discernible stop in the set position, with or without runners on base (Rule 8.01(b) note).
• Dropped ball on the mound: with runners on base, it's a ball to the batter. With no runners on, there's no penalty.
• Illegal pitch that is delivered: play continues as a delayed dead ball. When the play ends, the offensive manager may decline the illegal pitch and take the result of the play. If the batter reaches first safely and every runner advances at least one base, the play stands without reference to the illegal pitch.
• Chanting meant to cause an illegal pitch isn't allowed (Rule 4.06(c)). Teams may cheer for their own players, but not with artificial noisemakers or a deliberate crescendo as the pitcher delivers.

Calling an illegal pitch is a joint responsibility in a two-umpire crew.