In 2009, William Marotta donated sperm, free of charge, to a lesbian couple. Though Marotta signed a contract giving up financial responsibility for the child, the state of Kansas is now suing him for support after one of the mothers applied for financial assistance. NBC's Michelle Franzen reports.

A man who donated sperm to a pair of lesbians so they could start a family is now being hounded for child support by the state of Kansas — which refuses to recognize the same-sex coupling.

But William Marotta's attorneys want the now-separated lesbian co-parent to be involved in a lawsuit in which the state claims he is the legal father of a 3-year-old girl.

The state of Kansas contends that Marotta is legally responsible for the girl conceived after he responded to a Craigslist ad placed by the lesbian couple for sperm donation.

Kansas is seeking some $6,000 in back child support.

The ad was placed by Jennifer Schreiner and Angela Bauer more than three years ago with the idea that Marotta, a married mechanic from Topeka, would not be involved in the child’s life or bear any responsibility for her upbringing.

Marotta even signed a contract waiving parental rights and responsibilities — which he thought absolved him from any financial obligations for the child.

In fact, he didn’t even accept the $50 payment offered from Schreiner, who gave birth to the girl, and Bauer, Schreiner’s partner at the time.

The state of Kansas, however, sees it differently. The Sunflower State contends that the contract is invalid because a Kansas law requires that a licensed physician perform any artificial insemination — which was not the case with Schreiner.

Only Marotta and the birth mother, Schreiner, are party to the suit.

This week, attorneys for Bauer and Marotta asked a judge to reconsider a ruling that keeps Bauer out of the case as a full-fledged participant.

Bauer, they argue, who cares for the girl about half the time and signed the sperm donor agreement at issue, should be fully involved.

“The human beings in this case want all the adults in the case to make a determination for what is in the best interest of the child,” Joseph Booth, an attorney representing Bauer, told NBC News.

Booth said a recent Kansas high court case, Frazier v. Gouschaal, established that a nonbiological mother of children in a same-sex relationship has the same rights as a biological mother.

“The only basis to prevent Angela Bauer from the full status as a party is that she is female,” Booth wrote.

Benoit Swinnen, Marotta’s attorney, filed a similar motion on Tuesday seeking to make Bauer a “necessary party” or dismiss the case.

Swinnen claims the whole case is political, since neither of the lesbian parents has sought Marotta’s involvement and the money involved is “peanuts.”

“(The state) will do anything to push their traditional notion of families and suppress any nontraditional type of parenting,” Swinnen told NBC News. “It runs so contrary to the way the country is going.”

Swinnen’s Shawnee County District Court filing said Bauer should be allowed to intervene in the case and be recognized as the legal parent of the girl, not his client.

Schreiner as the birth parent has custody of the girl, but according to both attorneys Bauer takes care of the girl during the day with Schneiner caring for her in the evenings. Bauer and Scheiner have even drawn up a parenting plan for the girl, which Booth said, if and when it is approved by a court, would legally resolve issues of custody and financial support.

The state became involved in the case when the couple's relationship fell apart and the two broke up, and one of them got sick. They applied for state health insurance for the girl. The Kansas Department for Children and Families demanded they reveal the name of the sperm donor, which they eventually did, reluctantly.

The state then filed the child support claim against Marotta in October 2012.

Angela de Rocha, the communication director for Kansas’ DCF, wasn’t immediately available to comment on this week's filings, but in January she explained Kansas’ rationale for the lawsuit:

“In cases where the parties do not go through a licensed physician or a clinic, there remains the question of who actually is the father of the child or children. In such cases, DCF is required by statute to establish paternity and then pursue child support from the non-custodial parent,” Rocha said in a statement.

On Tuesday, District Court Judge Mary Mattivi appointed Jennifer Berger, a family law attorney, to represent Jennifer Schreiner.

Related: Hey, sperm donor, don't answer that Craigslist ad!