The Employee Free Choice Act, a proposed federal law that would change the way unions can be formed in the private sector, is casting an odd and confusing shadow over the Tom Allen-Susan Collins Senate race. Rep. Allen, the Democratic challenger, is an original co-sponsor of the measure. Sen. Collins, the incumbent Republican, opposes the legislation. Third party groups, the Coalition for a Democratic Workplace and Employee Freedom, have paid for TV ads criticizing Rep. Allen for supporting the bill. The coalition’s ad features an actor who played a mobster on the HBO series “The Sopranos.” Both Rep. Allen and Sen. Collins have denounced it.

An explanation of the law is in order, if only so TV viewers can understand the bizarre ads.

Under current law, someone working in the private sector who wants employees to join a union typically finds an existing union under which the business might fit. That union would then send a representative to meet with workers.

If the union representative gauges support for joining a union is strong, he then circulates “authorization cards” among the staff. The local worker typically gathers the cards, which are signed. If 30 percent of workers indicate they want a union, the employer is obligated to hold a secret ballot vote among employees. But typically, the process would not go forward unless at least 50 percent signed cards favoring a union, because union organizers know that many people will sign a card but not actually vote for a union.

If enough workers sign the card favoring a union, the union representative meets with the employer. The employer can simply agree to form a union, demand to see the cards, or call for a secret ballot election, which is supervised by the National Labor Relations Board. Labor relations lawyers generally advise employers not to look at the cards to avoid lawsuits that might come if a pro-union worker is fired and then claims retaliation was the motive.

After the cards are filed, the employer can hold meetings at which he can try to persuade workers against forming a union. The employer is not allowed to intimidate or coerce workers to vote against the union by promising better pay or benefits. About half the efforts at forming unions in the private sector in Maine fail.

Under the Employee Free Choice Act, which is now languishing in the Senate, if more than 50 percent of workers sign cards authorizing a union, the employer must begin negotiating with the new bargaining unit, and no secret ballot is required.

Opponents, such as Sen. Collins, argue it unfairly restrains the employer from making the case against a union and denies workers a pressure-free secret ballot vote. Proponents, such as Rep. Allen, argue the plight of middle class workers has eroded significantly is recent years, and the new law would help level the playing field to help employees get health insurance, pensions and job security.

Pro-union voters will likely agree with Rep. Allen, and anti-union voters will probably side with Sen. Collins, so the confusing ads aren’t likely to make much difference. And for what it’s worth: “Sopranos” actor Vincent Curatola, who appears in one of the ads, is a member of the Screen Actors Guild, a union.