Now that voters in Colorado and Washington have approved legalized sales of marijuana in those two states, the federal government is expected to aggressively confront the new laws through lawsuits saying they are invalidated under US law.

A potential showdown between state and federal authorities will probably not target individual users of the drug, instead focusing on new regulations that will make marijuana sales permissible, a violation of federal law.

“Federal law is federal law; it’s pretty black and white,” says Kevin Sabet, a former senior adviser at the White House Office of National Drug Control Policy in the Obama administration. “How it’s enforced, given resource constraints, is that small-scale users will likely not be targeted. But you’re going to see efforts by the Justice Department against large commercial grows or retail sales or states making money off the new laws.”

The measures passed last week in Washington State and Colorado both allow the recreational use of marijuana, but of more interest to federal authorities is that they require states to establish a system to license, regulate, and tax commercial retailers expected to sell the drug, including industrial hemp. Such a system would be much like what currently exists for the sales of alcohol and tobacco.

Under the new laws, the sale and possession of marijuana is restricted to adults 21 and older and does not apply to public use of the drug. The Colorado law also allows for a person to grow up to six marijuana plants for personal use in the privacy of his or her home, but forbids their sale.

So far, the US Department of Justice has not commented on what steps it might take against either state.

“In enacting the Controlled Substances Act, Congress determined that marijuana is a Schedule I controlled substance. We are reviewing the ballot initiative and have no additional comment at this time,” Justice Department spokeswoman Nanda Chitre told CBS News last week, referring to the Colorado measure.

An amendment will be added to the constitution of each state by January, but it will take time before lawmakers can create a regulatory system to establish how and where the drug can be sold, a process that may go into 2014.

“There’s no reason for the Feds to do anything instantly. There is time right now for consultation and deliberation for how to best proceed and for the states to persuade the federal government to give this time to develop,” says Ethan Nadelmann, executive director of the Drug Policy Alliance, an advocacy group based in New York City that helped campaign for the measures in Colorado and Washington.

Clues into how the Justice Department will approach the issue are in how it has dealt with state laws governing the sale of marijuana for medicinal use. Last week, Massachusetts became the 18th state since 1996 to legalize marijuana for health purposes. No individual has yet faced federal prosecution for personal use, but legal challenges in federal court have been waged in most states with medical marijuana laws on the books.

To what extent federal authorities crack down on states may depend on the strength of the regulatory system each has put into place, Mr. Nadelmann says. For example: California, the first state to pass the law, has the least developed system in place, leaving regulation to individual cities.

As a result, California has seen scattershot court rulings and federal involvement. In July, the Los Angeles City Council decided to close down most of the city’s storefront medical marijuana shops because it said their proliferation has made them too difficult to control. The city estimates that with 750 shops officially in operation and 200 more known to exist, it has more retailers selling marijuana than any other city in the United States.

Medical marijuana advocates launched lawsuits to block the ban, saying it was unconstitutional, which prompted the city to rescind the ban in October. Both city officials and advocates are appealing to the state for guidance on how to navigate inadequacies of state law regarding how to govern the market. The situation follows almost a year of Justice Department raids against some city marijuana shops that it says are fronts for drug traffickers.

However, Mr. Sabet says, the more states get involved in attempting to regulate the voter-approved marijuana market – whether for medical or recreation purposes – “the more they get in violation of the federal law.” That may pose an incentive to stall.

One thing is certain: Colorado and Washington are in a “wait and see” moment in reading the smoke signals from the Justice Department about next steps.

In a statement released last week, Colorado Attorney General John Suthers said that while he personally disagrees with the amendment’s passage, he is challenging the Justice Department “to make known its intentions regarding prosecution of activities sanctioned” by the amendment “as soon as possible in order to assist state regulators and the citizens of Colorado in making decisions about” its implementation.