In a German television interview, Martin Schulz said the treaty was not good in its current form, according to the BBC.
Schulz said the balance between copyright protection and the individual rights of internet users "is only very inadequately anchored in this agreement".
ACTA is aimed at improving the enforcement of intellectual property rights (IPR) by setting international standards for dealing with copyright infringements. Critics argue that it will lead to censorship of the internet, while supporters insist the agreement will not alter existing laws and will instead provide protection for content creators in the face of increasing levels of online piracy.
Over the weekend, thousands of people took part in coordinated marches across Europe, including the UK, in protest against ACTA, with the biggest protests in Germany, Poland and the Netherlands.
The protests came a week after about 2,000 people marched in the Slovenian capital, Ljubljana, and two weeks after thousands of people in Poland protested against ACTA when the country and 21 other European Union states, including the UK, signed the agreement.
Following the first protests in Poland, the country's prime minister, Donald Tusk, said he would hold off plans to ratify the agreement, admitting that the negotiation process "did not involve sufficient consultation".
Germany has held off from backing the agreement, citing the need for "further discussion", and Slovenia's ambassador to Japan, Helena Drnovsek Zorko, has apologized for her "carelessness" in signing the treaty on behalf of her country.
The UK's Intellectual Property Office maintains that ACTA should not mean new laws relating to internet use.
Signing ACTA is important for the UK, the IPO said, as it will set an international standard for tackling large-scale infringements of intellectual property rights through the creation of common enforcement standards and more effective international cooperation.
The treaty cannot be enacted before it is ratified by the European Parliament after a debate scheduled for June.
This article was first published by Computer Weekly