British MPs and Lords at the Assembly of the Council of Europe joined with colleagues to condemn the law, which was passed earlier this month.
Tory MP Tim Boswell, Labour peer Baroness Gale and Lib Dem MP Mike Hancock signed a written declaration, saying they are "shocked" that such information has been classified with the promotion of drugs or suicide, and the portrayal of killings, mutilation or torture.
They said the legislation will serve only to perpetuate discrimination and intolerance and deny young lesbian, gay and bisexual persons access to information which they need in order to live in accordance with their sexual orientation.
The written declaration calls on the the President of Lithuania to refer the law back to the Parliament for revision in the light of Lithuania’s international human rights obligations.
The 47-member Council of Europe predates the European Union.
It promotes and protects democracy, educational and sporting co-operation and created the European Court of Human Rights.
Members of the European Parliament have also condemned the new legislation, which requires the signature of the President of Lithuania to become law.
"It is my duty as an elected member of the European Parliament to act strongly against grave attempts to diminish human rights of EU citizens," said Michael Cashman, president of the European Parliament’s all-party Intergroup.
"This new law is a spit in the face of the European values.
"To limit freedom of expression based on homophobia is a clear breach of EU’s fundamental rights and principles."
Simon Maljevac, chairperson of the International Lesbian, Gay, Bisexual, Transgender and Queer Youth and Student Organisation, said:
"Our recent research, Social Exclusion of Young LGBT People in Europe, brought to light the fact that young gays and lesbians experience high levels of physical and psychological violence all over the European Union.
"We found that the highest levels occurred in schools. Similar surveys from other countries find that suicide rates among young LGBT people are up to 10 times higher than among their heterosexual fellows.
"All this suffering is caused by stigmatisation, intolerance and lack of access to information about homosexuality which young people need, both to understand their identity and to respect others differences. The new Lithuanian law will render even higher levels of suffering.
"We deplore the adoption of this law - it will harm young people, not protect them," Mr. Maljevac said.