The move comes in the wake of comments recently by government ministers in Germany and France, who have cast doubt on the deal.
German economy minister Sigmar Gabriel said he believes the deal is effectively dead.
Both the European Commission and the US responded by insisting that the TTIP negotiations remain on track and that intensive efforts are ongoing to conclude an ambitious agreement.
The 17 trade associations now publicly backing the talks include Amcham EU, Cefic, Digital Europe and BusinessEurope.
They have issued a joint statement which said, "It has been clear since the beginning of the negotiations that an ambitious and comprehensive agreement between the world's two largest economies will not be easy to achieve.
"Strong political commitment from the EU and US governments is necessary to deliver an agreement that boosts growth, competitiveness and jobs on both sides of the Atlantic. Continued and vocal support by EU and US political leaders is critical."
It went on, "A robust TTIP agreement could catalyse investment as well as trade in goods and services between the EU and U.S. markets. Businesses of all sizes, above all small companies, as well as workers, consumers, and citizens in both the EU and the U.S. could benefit.
"TTIP also provides a timely opportunity for the EU and U.S. to set the rules for trade and investment that could serve as a benchmark for the world."
However, a news conference in Parliament on Tuesday heard that both TTIP and a similar trade deal between the EU and Canada, called CETA, were of little value and should be scrapped.
Socialist deputy Sergio Cofferati said, "CETA negotiations have been conducted without the necessary public debate. The result is a very dangerous agreement which does not ensure a full respect of workers' rights and labour standards."
His comments were endorsed by GUE/NGL group MEP Fabio De Masi, who told reporters, "CETA is the little brother of TTIP and needs to be buried alongside it. The investment court system still undermines our justice system. A provisional application of CETA before decision of national parliaments is unacceptable."
Further comment came from French Greens/EFA group member Eva Joly who said, "The negotiation of new trade agreements putting multinational companies above choices of citizens would be an unbearable turning point for our democracies."
GUE/NGL group member Curzio Maltese agreed, adding, "CETA is nothing more than TTIP in disguise, and it is much more dangerous given how close it is to becoming implemented. The negotiation process has been utterly non-transparent and bereft of democratic scrutiny."
Three other MEPs spoke ahead of a public debate on TTIP in Parliament on Tuesday.
The "Progressive Caucus" debate, called "CETA, TTIP: two sides of the same coin?", counts former EU commissioner Pascal Lamy among the speakers.
The MEPs also speaking at the event include Socialist Guillaume Balas, who told this website, "It would be unacceptable to adopt CETA without having first informed MPs and citizens on the content of the agreement.
"In this sense, the Progressive Caucus debate aims to unite progressive European forces fighting for a democratic, fair and sustainable Europe."
Socialist member Emmanuel Maurel said, "CETA is the first stage of the EU's newest free-trade rocket, as well as the symbol of an irrational belief in deregulation and downwards harmonisation as privileged solutions to Europe's crises."
GUE/NGL group deputy added Dimitrios Papadimoulis commented, "We want to strengthen the dynamics of convergence, dialogue and unity in diversity."
The GUE/NGL group has also organised a debate on TTIP in Parliament on 15 November.