It's a shakedown!

Democrat big-city mayors are using taxpayer money as a weapon against guns. As they gathered in Washington, DC, for the Presidential inaugural, those mayors agreed to work toward a new goal: They want their police departments to buy guns and ammunition only from companies that will endorse Pres. Obama's gun control agenda.
It's the same bullying tactic used against Chick-fil-A, Wal-Mart, Whole Foods and others, except this time liberals want to do it with public money.
Purchasing laws typically require buying from a responsible vendor that offers the best quality and best price. Demanding that a company adopt a certain political position is wrong and quite possibly illegal as well.
More details are here.
The mayors' effort brings to mind a deal that Smith & Wesson made with the Clinton Administration in the year 2000 to change their products and marketing as and impose restrictions on those who sold their firearms. A boycott by gun owners resulted in a 40% drop in Smith & Wesson sales.
Only after the company was sold to a buyer who renounced the agreement did Smith & Wesson sales rebound.
Here is one history of that boycott.