Lawyers who falsely certify that they had witnessed the signing of a document, when in fact they had not, will be "visited with severe consequences".

The Court of Three Judges said this in written grounds released on Tuesday, explaining why it suspended a lawyer for 15 months over such "dishonest" conduct.

In the judgment, penned by Chief Justice Sundaresh Menon, the court emphasised that the gravity of such offences should not be understated. "Solicitors should ensure that they do not yield to the temptation to lower their guard just because they imagine that no harm will ensue."

The case involved sole proprietor Chia Choon Yang, who was called to the Bar in 1969. He voluntarily stopped practising last year.

In July 2015, Mr Chia was asked by a client, Mr David Li, to notarise a document - a power of attorney granted to Mr Li by a company known as New Eastern (1971).

The document authorised Mr Li to act on behalf of New Eastern to sign contracts and decide legal proceedings, among other things.

When Mr Chia saw the document, it already bore the signature of one of New Eastern's directors, Mr Loy Teu Wee.

After Mr Li told him that two other people had witnessed Mr Loy signing the power of attorney, Mr Chia added his signature and affixed his seal as a notary public on the document.

Mr Chia also prepared a notarial certificate stating that he had witnessed Mr Loy signing the power of attorney.

In April 2016, a director of New Eastern lodged a complaint against Mr Chia, after Mr Li purportedly used the power of attorney to enter into a contract with a Chinese company without New Eastern's knowledge or consent.

Before a disciplinary tribunal, Mr Chia admitted that his actions amounted to grossly improper conduct under the Legal Profession Act.

The tribunal found the case serious enough to be referred to the Court of Three Judges, which can suspend or disbar lawyers.

The Law Society, represented by Mr Joseph Liow, sought a suspension, arguing that actual harm had been caused because the document was used to enter into a contract.

It is unclear if New Eastern suffered any economic loss.

Mr Chia, represented by Senior Counsel Molly Lim, argued that a censure or fine was enough. He contended that there was no dishonesty.

In its judgment, the court said a notary public plays an important role in assuring the authenticity of documents and the identities of signatories.

"The failure to properly discharge such a role compromises public confidence in notaries public and inevitably in the legal profession as a whole."

The court found that Mr Chia's misconduct involved dishonesty, given that he had asserted a fact that he knew was untrue, knowing that others might rely on his statements in treating the document as genuine.

However, the court concluded that a striking off was not warranted.

There was neither a deception of the court nor a violation of the trust within a client-lawyer relationship, said the court. Mr Chia sincerely believed Mr Li and was not acting out of self-interest.

The court also noted his genuine remorse and that this was his first instance of misconduct in several decades of practice.