Food companies would be wise to join a voluntary program to cut salt — because otherwise, Washington will step in with regulations, Mayor Bloomberg warned yesterday.

The mayor offered the suggestion at a City Hall press conference where 16 firms — including Kraft and Heinz — announced that they had agreed to reduce salt in their products so that its consumption could be reduced 20 percent over the next five years.

“If you want federal regulation, a good way to get it is to not do something,” Bloomberg said.