The following is excerpted from Clifford Mishler’s Coins: Questions & Answers
Q: Was the minting of silver dollars suspended from 1928 until 1934 because the Treasury was overstocked with them?
A: Overstocking of unnecessary silver dollars was a normal condition during the reign of the powerful Western Silver Lobby. The Pittman Act, which authorized the melting of reserve silver dollars and sale of the bullion to Britain, also provided that the dollars disposed of be replaced with dollars coined from newly mined silver. Satisfaction of this stipulation was achieved by April of 1928, at which time the minting of silver dollars ceased. The 1934 and 1935 mintages were carried out under an executive proclamation.