Directly from the NFL rulebook:
Item 4: Unsportsmanlike Conduct. An attempt to call an excess team timeout or to call a second
timeout in the same dead-ball period by Team B in an attempt to “freeze” a kicker, will be considered
unsportsmanlike conduct and will subject the offending team to a 15-yard penalty (See 12-3). This will
apply to field goal or Try attempts.
Note: If an attempt is made to call a timeout in such situations, the officials shall not grant a timeout; instead,
play will continue, and a penalty will be called, with customary enforcement. If a timeout is inadvertently
granted, the penalty shall also be enforced. See 12-3-1-v.