PORTLAND — Lawyers for 15 sex offenders are challenging the constitutionality of Maine’s sex offender registry law before the state’s supreme court on Thursday.

The appellants, who retain their anonymity under “John Doe” aliases, argue, among other things, that the law is unconstitutionally retroactive and violates their due process and civil rights.

The case stretches back to 2006. Soon after John Doe I was notified that he was required to register as a sex offender, a Canadian man randomly killed two Maine sex offender registrants. John Doe I then filed his suit.

Similar cases were consolidated, and there was, at one point, as many as 47 John Does.

Some dropped out of the case after the Legislature changed the law to address a 2009 state supreme court decision that found some portions violated the prohibition on retroactive laws. Some offenders were able to get off the registry if they had been convicted between Jan. 1, 1982 and June 30, 1992 and met certain requirements, including having no subsequent felony offenses.

Sex offenders have been required to register with the state since 1999. The registry went online in 2003.